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<p>Ce tutoriel explore d’autres concepts de Numpy, tels que les données catégorielles, l’indexation avancée et le traitement des données non chiffrées (NaN).</p>
<p>Suivez les instructions ci-dessous pour télécharger le tutoriel et l’ouvrir dans le Sandbox.</p>
<section id="Download-the-tutorial-notebook" style="box-sizing: border-box; color: #000000;">
<h2 style="box-sizing: border-box; margin-top: 0px; font-weight: bold; font-size: 24px; color: #336699; text-align: left;">TÉLÉCHARGER LE NOTEBOOK</h2>
<p style="box-sizing: border-box; line-height: 24px; margin: 0px 0px 24px; font-size: 16px; text-align: left;"><a class="reference external" href="/assets/courseware/v1/38aca23d0de6ee7f7c20240e93e6bf4b/asset-v1:digitalearthafrica+DEA101-fr+2021+type@asset+block/04_download-cleaning_data.ipynb" style="box-sizing: border-box; color: #3091d1; text-decoration-line: none; cursor: pointer; outline: 0px;" target="[object Object]">Télécharger le notebook du tutoriel Python basics 4</a></p>
<p style="box-sizing: border-box; line-height: 24px; margin: 0px 0px 24px; font-size: 16px; text-align: left;">Pour visualiser ce notebook sur le Sandbox, vous devrez d’abord le télécharger sur votre ordinateur, puis le charger sur le Sandbox. Assurez-vous d’avoir suivi les prérequis de configuration listés dans <a class="reference internal" href="/courses/course-v1:digitalearthafrica+DEA101-fr+2021/jump_to_id/9c210d02e6fe484a8ce67c67a1e9c2fa" target="[object Object]" style="box-sizing: border-box; color: #2980b9; text-decoration-line: none; cursor: pointer;">Les Bases de Python 1 : Jupyter</a>, puis suivez ces instructions :</p>
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<p style="text-align: left; box-sizing: border-box; line-height: 24px; margin: 0px; font-size: 16px;">Téléchargez le notebook en cliquant sur le lien ci-dessus.</p>
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<p style="text-align: left; box-sizing: border-box; line-height: 24px; margin: 0px; font-size: 16px;">Dans le Sandbox, ouvrez le dossier <strong>Training</strong>.</p>
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<p style="text-align: left; box-sizing: border-box; line-height: 24px; margin: 0px; font-size: 16px;">Cliquez sur le bouton <strong>Transférer les fichiers</strong> comme indiqué ci-dessous.</p>
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<p style="box-sizing: border-box; line-height: 24px; margin: 0px 0px 24px; font-size: 16px; text-align: left;"><img alt="Upload button." class="no-scaled-link" src="https://learn.digitalearthafrica.org/asset-v1:digitalearthafrica+DEA101+2021+type@asset+block@05_solution_uploadbutton.png" style="box-sizing: border-box; border: 0px; vertical-align: middle; width: 400px;" /></p>
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<p style="text-align: left; box-sizing: border-box; line-height: 24px; margin: 0px; font-size: 16px;">Sélectionnez le notebook téléchargé à l’aide du navigateur de fichiers. Cliquez sur <strong>OK</strong>.</p>
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<p style="text-align: left; box-sizing: border-box; line-height: 24px; margin: 0px; font-size: 16px;">Le notebook de solutions apparaîtra dans le dossier <strong>Training</strong>. Double-cliquez dessus pour l’ouvrir.</p>
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<p style="box-sizing: border-box; line-height: 24px; margin: 0px 0px 24px; font-size: 16px; text-align: left;">Vous pouvez maintenant utiliser le notebook d’exercices comme une version interactive de cette page Web.</p>
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<p class="admonition-title" style="box-sizing: border-box; line-height: 1; margin: -12px -12px 12px; font-size: inherit; font-family: inherit; font-variant-numeric: normal; font-variant-east-asian: normal; font-weight: bold; font-stretch: normal; text-rendering: auto; -webkit-font-smoothing: antialiased; color: #ffffff; background: #6ab0de; padding: 6px 12px; text-align: left;">Note</p>
<p style="box-sizing: border-box; line-height: 24px; margin: 0px; font-size: 16px; text-align: left;">Le notebook devrait ressembler au texte et au code ci-dessous. Cependant, les sorties du notebook d’exercices sont vides (c’est-à-dire qu’aucun résultat n’apparaît après les cellules de code). Suivez les instructions du cahier pour exécuter les cellules du notebook d’exercices. Reportez-vous à cette page pour vérifier que vos résultats sont similaires.</p>
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<p>Nous allons introduire une structure numpy appelée <strong>dictionnaire</strong>. Cela sera utile pour la prochaine leçon sur <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">xarray</span></code>.</p>
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<h3 style="text-align: left;">Clés et valeurs</h3>
<p style="text-align: left;">Un dictionnaire représente une correspondance entre <strong>clés</strong> et <strong>valeurs</strong>. Les clés et les valeurs sont des objets Python de n’importe quel type. On déclare un dictionnaire en utilisant des accolades <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">{}</span></code>. A l’intérieur, on spécifie la clé puis la valeur qui lui est associée, les clés et les valeurs étant séparées par un deux-points <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">:</span></code>. Les virgules<code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">,</span></code> sont utilisées pour séparer les éléments du dictionnaire.</p>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 12px; overflow: auto;"><span style="box-sizing: border-box;"></span><span class="n" style="box-sizing: border-box;">dictionary_name</span> <span class="o" style="box-sizing: border-box; color: #666666;">=</span> <span class="p" style="box-sizing: border-box;">{</span><span class="n" style="box-sizing: border-box;">key1</span><span class="p" style="box-sizing: border-box;">:</span> <span class="n" style="box-sizing: border-box;">value1</span><span class="p" style="box-sizing: border-box;">,</span> <span class="n" style="box-sizing: border-box;">key2</span><span class="p" style="box-sizing: border-box;">:</span> <span class="n" style="box-sizing: border-box;">value2</span><span class="p" style="box-sizing: border-box;">,</span> <span class="n" style="box-sizing: border-box;">key3</span><span class="p" style="box-sizing: border-box;">:</span> <span class="n" style="box-sizing: border-box;">value3</span><span class="p" style="box-sizing: border-box;">}</span>
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<p style="text-align: left;">Par exemple :</p>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 0px; overflow: hidden; border: none; box-shadow: none; background: none; color: #307fc1;"><span style="box-sizing: border-box; border: none; padding: 0px; margin: 0px; box-shadow: none; background: none;"></span>[ ]:
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="n" style="box-sizing: border-box;">d</span> <span class="o" style="box-sizing: border-box; color: #666666;">=</span> <span class="p" style="box-sizing: border-box;">{</span><span class="mi" style="box-sizing: border-box; color: #666666;">1</span><span class="p" style="box-sizing: border-box;">:</span> <span class="s1" style="box-sizing: border-box; color: #ba2121;">'one'</span><span class="p" style="box-sizing: border-box;">,</span>
<span class="mi" style="box-sizing: border-box; color: #666666;">2</span><span class="p" style="box-sizing: border-box;">:</span> <span class="s1" style="box-sizing: border-box; color: #ba2121;">'two'</span><span class="p" style="box-sizing: border-box;">,</span>
<span class="mi" style="box-sizing: border-box; color: #666666;">3</span><span class="p" style="box-sizing: border-box;">:</span> <span class="s1" style="box-sizing: border-box; color: #ba2121;">'apple'</span><span class="p" style="box-sizing: border-box;">}</span>
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<p style="text-align: left;">Dans le dictionnaire <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">d</span></code> ci-dessus, nous avons trois <strong>clés</strong> <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">1</span></code>, <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">2</span></code>, <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">3</span></code>, et leurs <strong>valeurs</strong> respectives <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">'one'</span></code>, <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">'two'</span></code> et<code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">'apple'</span></code>.</p>
<p style="text-align: left;">Nous pouvons rechercher des éléments dans un dictionnaire en utilisant la syntaxe <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">[</span> <span class="pre" style="box-sizing: border-box;">key_name</span> <span class="pre" style="box-sizing: border-box;">]</span></code> pour adresser la valeur stockée sous une clé. La syntaxe est la suivante :</p>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 12px; overflow: auto;"><span style="box-sizing: border-box;"></span><span class="n" style="box-sizing: border-box;">dictionary_name</span><span class="p" style="box-sizing: border-box;">[</span><span class="n" style="box-sizing: border-box;">key_name</span><span class="p" style="box-sizing: border-box;">]</span>
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<p style="text-align: left;">Dans notre exemple de dictionnaire <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">d</span></code> ci-dessus, nous pouvons appeler la valeur associée au nom de clé <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">1</span></code> comme suit :</p>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 12px; overflow: auto;"><span style="box-sizing: border-box;"></span><span class="n" style="box-sizing: border-box;">d</span><span class="p" style="box-sizing: border-box;">[</span><span class="mi" style="box-sizing: border-box; color: #666666;">1</span><span class="p" style="box-sizing: border-box;">]</span>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="nb" style="box-sizing: border-box; color: #008000;">print</span><span class="p" style="box-sizing: border-box;">(</span><span class="n" style="box-sizing: border-box;">d</span><span class="p" style="box-sizing: border-box;">[</span><span class="mi" style="box-sizing: border-box; color: #666666;">1</span><span class="p" style="box-sizing: border-box;">],</span> <span class="s2" style="box-sizing: border-box; color: #ba2121;">" + "</span><span class="p" style="box-sizing: border-box;">,</span> <span class="n" style="box-sizing: border-box;">d</span><span class="p" style="box-sizing: border-box;">[</span><span class="mi" style="box-sizing: border-box; color: #666666;">2</span><span class="p" style="box-sizing: border-box;">],</span> <span class="s2" style="box-sizing: border-box; color: #ba2121;">" = "</span><span class="p" style="box-sizing: border-box;">,</span> <span class="n" style="box-sizing: border-box;">d</span><span class="p" style="box-sizing: border-box;">[</span><span class="mi" style="box-sizing: border-box; color: #666666;">3</span><span class="p" style="box-sizing: border-box;">])</span>
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<p style="text-align: left;">Les éléments d’un dictionnaire peuvent être modifiés ou de nouveaux éléments peuvent être ajoutés en utilisant la syntaxe <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">nom_du_dictionnaire[nom_de_la_clé] = valeur</span></code>.</p>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><font color="#000000" face="SFMono-Regular, Menlo, Monaco, Consolas, Liberation Mono, Courier New, Courier, monospace"><span style="box-sizing: border-box;"></span></font><span class="n" style="box-sizing: border-box;">d</span><span class="p" style="box-sizing: border-box;">[</span><span class="mi" style="box-sizing: border-box; color: #666666;">3</span><span class="p" style="box-sizing: border-box;">]</span><font color="#000000" face="SFMono-Regular, Menlo, Monaco, Consolas, Liberation Mono, Courier New, Courier, monospace"><span style="font-size: 12px; white-space: pre;"> </span></font><span class="o" style="box-sizing: border-box; color: #666666;">=</span><font color="#000000" face="SFMono-Regular, Menlo, Monaco, Consolas, Liberation Mono, Courier New, Courier, monospace"><span style="font-size: 12px; white-space: pre;"> </span></font><span class="s1" style="box-sizing: border-box; color: #ba2121;">'three'</span><font color="#000000" face="SFMono-Regular, Menlo, Monaco, Consolas, Liberation Mono, Courier New, Courier, monospace"><span style="font-size: 12px; white-space: pre;">
</span></font><span class="n" style="box-sizing: border-box;">d</span><span class="p" style="box-sizing: border-box;">[</span><span class="mi" style="box-sizing: border-box; color: #666666;">4</span><span class="p" style="box-sizing: border-box;">]</span><font color="#000000" face="SFMono-Regular, Menlo, Monaco, Consolas, Liberation Mono, Courier New, Courier, monospace"><span style="font-size: 12px; white-space: pre;"> </span></font><span class="o" style="box-sizing: border-box; color: #666666;">=</span><font color="#000000" face="SFMono-Regular, Menlo, Monaco, Consolas, Liberation Mono, Courier New, Courier, monospace"><span style="font-size: 12px; white-space: pre;"> </span></font><span class="s1" style="box-sizing: border-box; color: #ba2121;">'four'</span><font color="#000000" face="SFMono-Regular, Menlo, Monaco, Consolas, Liberation Mono, Courier New, Courier, monospace"><span style="font-size: 12px; white-space: pre;">
</span></font><span class="nb" style="box-sizing: border-box; color: #008000;">print</span><span class="p" style="box-sizing: border-box;">(</span><span class="n" style="box-sizing: border-box;">d</span><span class="p" style="box-sizing: border-box;">[</span><span class="mi" style="box-sizing: border-box; color: #666666;">1</span><span class="p" style="box-sizing: border-box;">],</span><font color="#000000" face="SFMono-Regular, Menlo, Monaco, Consolas, Liberation Mono, Courier New, Courier, monospace"><span style="font-size: 12px; white-space: pre;"> </span></font><span class="s2" style="box-sizing: border-box; color: #ba2121;">" + "</span><span class="p" style="box-sizing: border-box;">,</span><font color="#000000" face="SFMono-Regular, Menlo, Monaco, Consolas, Liberation Mono, Courier New, Courier, monospace"><span style="font-size: 12px; white-space: pre;"> </span></font><span class="n" style="box-sizing: border-box;">d</span><span class="p" style="box-sizing: border-box;">[</span><span class="mi" style="box-sizing: border-box; color: #666666;">2</span><span class="p" style="box-sizing: border-box;">],</span><font color="#000000" face="SFMono-Regular, Menlo, Monaco, Consolas, Liberation Mono, Courier New, Courier, monospace"><span style="font-size: 12px; white-space: pre;"> </span></font><span class="s2" style="box-sizing: border-box; color: #ba2121;">" = "</span><span class="p" style="box-sizing: border-box;">,</span><font color="#000000" face="SFMono-Regular, Menlo, Monaco, Consolas, Liberation Mono, Courier New, Courier, monospace"><span style="font-size: 12px; white-space: pre;"> </span></font><span class="n" style="box-sizing: border-box;">d</span><span class="p" style="box-sizing: border-box;">[</span><span class="mi" style="box-sizing: border-box; color: #666666;">3</span><span class="p" style="box-sizing: border-box;">])</span><font face="Open Sans, Verdana, Arial, Helvetica, sans-serif"><span style="white-space: normal;">
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<p>Là encore, le nom du dictionnaire, le nom de la clé et la valeur doivent être spécifiés.</p>
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<h3>Classification des données avec des dictionnaires</h3>
<p>Les dictionnaires sont utiles pour l’analyse des données (y compris l’analyse des données satellitaires) car ils permettent d’attribuer facilement des<strong> valeurs catégorielles</strong> à notre ensemble de données. La télédétection peut être utilisée pour créer des produits de classification qui utilisent des valeurs catégorielles. Ces produits ne contiennent pas de valeurs continues. Ils utilisent des valeurs discrètes pour représenter les différentes classes auxquelles les pixels individuels peuvent appartenir.</p>
<p>À titre d’exemple, les cellules suivantes simulent une image très simple contenant trois types de couverture végétale différents. La valeur <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">1</span></code><span style="font-size: 1em;"> représente la zone couverte d’herbe (grass), </span><code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">2</span></code><span style="font-size: 1em;"> les terres cultivées (crops) et </span><code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">3</span></code><span style="font-size: 1em;"> la ville (city).</span></p>
<p>Tout d’abord, nous importons les bibliothèques que nous voulons utiliser.</p>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="o" style="box-sizing: border-box; color: #666666;">%</span><span class="k" style="box-sizing: border-box; color: #008000; font-weight: bold;">matplotlib</span> inline
<span class="kn" style="box-sizing: border-box; color: #008000; font-weight: bold;">import</span> <span class="nn" style="box-sizing: border-box; color: #0000ff; font-weight: bold;">numpy</span> <span class="k" style="box-sizing: border-box; color: #008000; font-weight: bold;">as</span> <span class="nn" style="box-sizing: border-box; color: #0000ff; font-weight: bold;">np</span>
<span class="kn" style="box-sizing: border-box; color: #008000; font-weight: bold;">from</span> <span class="nn" style="box-sizing: border-box; color: #0000ff; font-weight: bold;">matplotlib</span> <span class="kn" style="box-sizing: border-box; color: #008000; font-weight: bold;">import</span> <span class="n" style="box-sizing: border-box;">pyplot</span> <span class="k" style="box-sizing: border-box; color: #008000; font-weight: bold;">as</span> <span class="n" style="box-sizing: border-box;">plt</span>
<span class="kn" style="box-sizing: border-box; color: #008000; font-weight: bold;">from</span> <span class="nn" style="box-sizing: border-box; color: #0000ff; font-weight: bold;">matplotlib</span> <span class="kn" style="box-sizing: border-box; color: #008000; font-weight: bold;">import</span> <span class="n" style="box-sizing: border-box;">colors</span>
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<p>Nous allons maintenant créer un tableau numpy bidimensionnel de 100 pixels x 100 pixels où chaque valeur est égale à <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">1</span></code>. Ceci est fait en utilisant la fonction <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">numpy.ones</span></code>. Ensuite, nous utilisons l’indexation de tableau pour attribuer à une partie de la zone la valeur <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">2</span></code>, et à une autre partie la valeur <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">3</span></code>.</p>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># grass = 1</span>
<span class="n" style="box-sizing: border-box;">area</span> <span class="o" style="box-sizing: border-box; color: #666666;">=</span> <span class="n" style="box-sizing: border-box;">np</span><span class="o" style="box-sizing: border-box; color: #666666;">.</span><span class="n" style="box-sizing: border-box;">ones</span><span class="p" style="box-sizing: border-box;">((</span><span class="mi" style="box-sizing: border-box; color: #666666;">100</span><span class="p" style="box-sizing: border-box;">,</span><span class="mi" style="box-sizing: border-box; color: #666666;">100</span><span class="p" style="box-sizing: border-box;">))</span>
<span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># crops = 2</span>
<span class="n" style="box-sizing: border-box;">area</span><span class="p" style="box-sizing: border-box;">[</span><span class="mi" style="box-sizing: border-box; color: #666666;">10</span><span class="p" style="box-sizing: border-box;">:</span><span class="mi" style="box-sizing: border-box; color: #666666;">60</span><span class="p" style="box-sizing: border-box;">,</span><span class="mi" style="box-sizing: border-box; color: #666666;">20</span><span class="p" style="box-sizing: border-box;">:</span><span class="mi" style="box-sizing: border-box; color: #666666;">50</span><span class="p" style="box-sizing: border-box;">]</span> <span class="o" style="box-sizing: border-box; color: #666666;">=</span> <span class="mi" style="box-sizing: border-box; color: #666666;">2</span>
<span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># city = 3</span>
<span class="n" style="box-sizing: border-box;">area</span><span class="p" style="box-sizing: border-box;">[</span><span class="mi" style="box-sizing: border-box; color: #666666;">70</span><span class="p" style="box-sizing: border-box;">:</span><span class="mi" style="box-sizing: border-box; color: #666666;">90</span><span class="p" style="box-sizing: border-box;">,</span><span class="mi" style="box-sizing: border-box; color: #666666;">60</span><span class="p" style="box-sizing: border-box;">:</span><span class="mi" style="box-sizing: border-box; color: #666666;">80</span><span class="p" style="box-sizing: border-box;">]</span> <span class="o" style="box-sizing: border-box; color: #666666;">=</span> <span class="mi" style="box-sizing: border-box; color: #666666;">3</span>
<span class="n" style="box-sizing: border-box;">area</span><span class="o" style="box-sizing: border-box; color: #666666;">.</span><span class="n" style="box-sizing: border-box;">shape</span><span class="p" style="box-sizing: border-box;">,</span> <span class="n" style="box-sizing: border-box;">area</span><span class="o" style="box-sizing: border-box; color: #666666;">.</span><span class="n" style="box-sizing: border-box;">dtype</span>
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<p>Nous avons maintenant une matrice remplie de 1, 2 et 3. À ce stade, il n’y a pas d’association entre les chiffres et les différents types de couverture végétale.</p>
<p>Si nous voulons montrer à quoi ressemble la zone selon la désignation herbe/cultures/ville, nous pouvons donner une couleur à chacune des classifications.</p>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># We map the values to colours</span>
<span class="n" style="box-sizing: border-box;">index</span> <span class="o" style="box-sizing: border-box; color: #666666;">=</span> <span class="p" style="box-sizing: border-box;">{</span><span class="mi" style="box-sizing: border-box; color: #666666;">1</span><span class="p" style="box-sizing: border-box;">:</span> <span class="s1" style="box-sizing: border-box; color: #ba2121;">'green'</span><span class="p" style="box-sizing: border-box;">,</span> <span class="mi" style="box-sizing: border-box; color: #666666;">2</span><span class="p" style="box-sizing: border-box;">:</span> <span class="s1" style="box-sizing: border-box; color: #ba2121;">'yellow'</span><span class="p" style="box-sizing: border-box;">,</span> <span class="mi" style="box-sizing: border-box; color: #666666;">3</span><span class="p" style="box-sizing: border-box;">:</span> <span class="s1" style="box-sizing: border-box; color: #ba2121;">'grey'</span><span class="p" style="box-sizing: border-box;">}</span>
<span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># Create a discrete colour map</span>
<span class="n" style="box-sizing: border-box;">cmap</span> <span class="o" style="box-sizing: border-box; color: #666666;">=</span> <span class="n" style="box-sizing: border-box;">colors</span><span class="o" style="box-sizing: border-box; color: #666666;">.</span><span class="n" style="box-sizing: border-box;">ListedColormap</span><span class="p" style="box-sizing: border-box;">(</span><span class="n" style="box-sizing: border-box;">index</span><span class="o" style="box-sizing: border-box; color: #666666;">.</span><span class="n" style="box-sizing: border-box;">values</span><span class="p" style="box-sizing: border-box;">())</span>
<span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># Plot</span>
<span class="n" style="box-sizing: border-box;">plt</span><span class="o" style="box-sizing: border-box; color: #666666;">.</span><span class="n" style="box-sizing: border-box;">imshow</span><span class="p" style="box-sizing: border-box;">(</span><span class="n" style="box-sizing: border-box;">area</span><span class="p" style="box-sizing: border-box;">,</span> <span class="n" style="box-sizing: border-box;">cmap</span><span class="o" style="box-sizing: border-box; color: #666666;">=</span><span class="n" style="box-sizing: border-box;">cmap</span><span class="p" style="box-sizing: border-box;">)</span>
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<p>Dans le cas ci-dessus, chaque pixel avait une valeur soit de <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">1</span></code>, <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">2</span></code> ou <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">3</span></code>. Que se passe-t-il si notre jeu de données est incomplet et qu’il n’y a pas de données à certains endroits ?</p>
<h3></h3>
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<h3>Données manquantes</h3>
<p>C’est un problème courant dans les ensembles de données réelles. Les ensembles de données réelles peuvent être incomplets et il peut manquer des données à certains moments ou endroits. Pour y remédier, nous utilisons la valeur spéciale <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">NaN</span></code>, qui signifie <strong style="box-sizing: border-box;">Not a Number</strong>.</p>
<p>Les <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">NaNs</span></code> sont désignés par la fonction numpy <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">np.nan</span></code>.</p>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="n" style="box-sizing: border-box;">arr</span> <span class="o" style="box-sizing: border-box; color: #666666;">=</span> <span class="n" style="box-sizing: border-box;">np</span><span class="o" style="box-sizing: border-box; color: #666666;">.</span><span class="n" style="box-sizing: border-box;">array</span><span class="p" style="box-sizing: border-box;">([</span><span class="mi" style="box-sizing: border-box; color: #666666;">1</span><span class="p" style="box-sizing: border-box;">,</span><span class="mi" style="box-sizing: border-box; color: #666666;">2</span><span class="p" style="box-sizing: border-box;">,</span><span class="mi" style="box-sizing: border-box; color: #666666;">3</span><span class="p" style="box-sizing: border-box;">,</span><span class="mi" style="box-sizing: border-box; color: #666666;">4</span><span class="p" style="box-sizing: border-box;">,</span><span class="mi" style="box-sizing: border-box; color: #666666;">5</span><span class="p" style="box-sizing: border-box;">,</span><span class="n" style="box-sizing: border-box;">np</span><span class="o" style="box-sizing: border-box; color: #666666;">.</span><span class="n" style="box-sizing: border-box;">nan</span><span class="p" style="box-sizing: border-box;">,</span><span class="mi" style="box-sizing: border-box; color: #666666;">7</span><span class="p" style="box-sizing: border-box;">,</span><span class="mi" style="box-sizing: border-box; color: #666666;">8</span><span class="p" style="box-sizing: border-box;">,</span><span class="mi" style="box-sizing: border-box; color: #666666;">9</span><span class="p" style="box-sizing: border-box;">],</span> <span class="n" style="box-sizing: border-box;">dtype</span><span class="o" style="box-sizing: border-box; color: #666666;">=</span><span class="n" style="box-sizing: border-box;">np</span><span class="o" style="box-sizing: border-box; color: #666666;">.</span><span class="n" style="box-sizing: border-box;">float32</span><span class="p" style="box-sizing: border-box;">)</span>
<span class="n" style="box-sizing: border-box;">arr</span>
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<p>Pour calculer des statistiques sur des tableaux contenant des valeurs NaN, numpy possède des versions spéciales de fonctions communes telles que <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">mean</span></code>, l’écart-type <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">std</span></code>, et <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">sum</span></code> qui ignorent les valeurs <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">NaN</span></code> values. Par exemple, la cellule suivante montre la différence entre l’utilisation de la fonction habituelle <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">mean</span></code> et la fonction <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">nanmean</span></code>.</p>
<p>La fonction <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">mean</span></code> ne peut pas gérer les valeurs <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">NaN</span></code> elle renvoie donc <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">nan</span></code>. La fonction<code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">nanmean</span></code> n’inclut pas les valeurs <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">NaN</span></code> dans le calcul, et renvoie donc une valeur numérique.</p>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 0px; overflow: hidden; border: none; box-shadow: none; background: none; color: #307fc1;"><span style="box-sizing: border-box; border: none; padding: 0px; margin: 0px; box-shadow: none; background: none;"></span>[9]:
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="nb" style="box-sizing: border-box; color: #008000;">print</span><span class="p" style="box-sizing: border-box;">(</span><span class="n" style="box-sizing: border-box;">np</span><span class="o" style="box-sizing: border-box; color: #666666;">.</span><span class="n" style="box-sizing: border-box;">mean</span><span class="p" style="box-sizing: border-box;">(</span><span class="n" style="box-sizing: border-box;">arr</span><span class="p" style="box-sizing: border-box;">))</span>
<span class="nb" style="box-sizing: border-box; color: #008000;">print</span><span class="p" style="box-sizing: border-box;">(</span><span class="n" style="box-sizing: border-box;">np</span><span class="o" style="box-sizing: border-box; color: #666666;">.</span><span class="n" style="box-sizing: border-box;">nanmean</span><span class="p" style="box-sizing: border-box;">(</span><span class="n" style="box-sizing: border-box;">arr</span><span class="p" style="box-sizing: border-box;">))</span>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: pre; line-height: normal; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none; background: unset;">nan
4.875
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<p></p>
<p></p>
<p>Notez que <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">NaN</span></code> n’est généralement pas utilisé comme clé dans les entrées clé-valeur des dictionnaires car il existe différentes façons d’exprimer <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">NaN</span></code> en Python et elles ne sont pas toujours équivalentes. Cependant, il est toujours possible de visualiser des données avec des <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">NaN</span></code>; il y aura des vides dans l’image où il n’y a pas de données.</p>
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<section id="Exercises" style="box-sizing: border-box;">
<section id="4.1-The-harvesting-season-has-arrived-and-our-cropping-lands-have-changed-colour-to-brown.-Can-you:" style="box-sizing: border-box;">
<h3 style="box-sizing: border-box; margin-top: 0px; font-weight: bold; font-size: 20px; color: #336699; text-align: left;">4.1 La saison des récoltes est arrivée et nos terres cultivées ont changé de couleur pour devenir brunes. Pouvez-vous :<a class="headerlink" href="https://training.digitalearthafrica.org/en/latest/python_basics/04_cleaning_data.html#4.1-The-harvesting-season-has-arrived-and-our-cropping-lands-have-changed-colour-to-brown.-Can-you:" title="Permalink to this headline" style="box-sizing: border-box; color: #2980b9; text-decoration-line: none; cursor: pointer; display: inline-block; font-variant-numeric: normal; font-variant-east-asian: normal; font-weight: normal; font-stretch: normal; line-height: 1; font-family: inherit; font-size: 14px; text-rendering: auto; -webkit-font-smoothing: antialiased; visibility: hidden;"></a></h3>
<section id="4.1.1-Modify-the-yellow-area-to-contain-the-new-value-4?" style="box-sizing: border-box;">
<h4 style="box-sizing: border-box; font-size: 18.4px; color: #336699;">4.1.1 Modifiez la zone jaune pour contenir la nouvelle valeur <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 13.8px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">4</span></code>?<a class="headerlink" href="https://training.digitalearthafrica.org/en/latest/python_basics/04_cleaning_data.html#4.1.1-Modify-the-yellow-area-to-contain-the-new-value-4?" title="Permalink to this headline" style="box-sizing: border-box; color: #2980b9; text-decoration-line: none; cursor: pointer; display: inline-block; font-variant-numeric: normal; font-variant-east-asian: normal; font-weight: normal; font-stretch: normal; line-height: 1; font-family: inherit; font-size: 14px; text-rendering: auto; -webkit-font-smoothing: antialiased; visibility: hidden;"></a></h4>
</section>
<section id="4.1.2-Add-a-new-entry-to-the-index-dictionary-mapping-number-4-to-the-value-brown." style="box-sizing: border-box;">
<h4 style="box-sizing: border-box; font-size: 18.4px; color: #336699;">4.1.2 Ajoutez une nouvelle entrée au dictionnaire <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 13.8px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">index</span></code> den associant le numéro <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 13.8px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">4</span></code> à la valeur <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 13.8px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">brown</span></code>.<a class="headerlink" href="https://training.digitalearthafrica.org/en/latest/python_basics/04_cleaning_data.html#4.1.2-Add-a-new-entry-to-the-index-dictionary-mapping-number-4-to-the-value-brown." title="Permalink to this headline" style="box-sizing: border-box; color: #2980b9; text-decoration-line: none; cursor: pointer; display: inline-block; font-variant-numeric: normal; font-variant-east-asian: normal; font-weight: normal; font-stretch: normal; line-height: 1; font-family: inherit; font-size: 14px; text-rendering: auto; -webkit-font-smoothing: antialiased; visibility: hidden;"></a></h4>
</section>
<section id="4.1.3-Plot-the-area." style="box-sizing: border-box;">
<h4 style="box-sizing: border-box; font-size: 18.4px; color: #336699;">4.1.3 Affichez la zone.<a class="headerlink" href="https://training.digitalearthafrica.org/en/latest/python_basics/04_cleaning_data.html#4.1.3-Plot-the-area." title="Permalink to this headline" style="box-sizing: border-box; color: #2980b9; text-decoration-line: none; cursor: pointer; display: inline-block; font-variant-numeric: normal; font-variant-east-asian: normal; font-weight: normal; font-stretch: normal; line-height: 1; font-family: inherit; font-size: 14px; text-rendering: auto; -webkit-font-smoothing: antialiased; visibility: hidden;"></a></h4>
<div class="nbinput nblast docutils container" style="box-sizing: border-box; display: flex; align-items: flex-start; margin: 0px 0px 19px; width: 696.469px; padding-top: 5px; padding-bottom: 5px;">
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 16px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 0px; overflow: hidden; border: none; box-shadow: none; background: none; color: #307fc1;"><span style="box-sizing: border-box; border: none; padding: 0px; margin: 0px; box-shadow: none; background: none;"></span>[ ]:
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<div class="input_area highlight-ipython3 notranslate" style="box-sizing: border-box; margin: 0px; flex: 1 1 0%; overflow: auto; border: 1px solid #e0e0e0; border-radius: 2px;">
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 16px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># 4.1.1 Modifiez la zone jaune pour garder la valeur 4</span>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 16px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 0px; overflow: hidden; border: none; box-shadow: none; background: none; color: #307fc1;"><span style="box-sizing: border-box; border: none; padding: 0px; margin: 0px; box-shadow: none; background: none;"></span>[ ]:
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<div class="input_area highlight-ipython3 notranslate" style="box-sizing: border-box; margin: 0px; flex: 1 1 0%; overflow: auto; border: 1px solid #e0e0e0; border-radius: 2px;">
<div class="highlight" style="box-sizing: border-box; background: #f8f8f8; border: none; overflow: auto hidden; margin: 0px; padding: 0px; box-shadow: none;">
<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 16px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># 4.1.2 Ajouter une nouvelle paire clé-valeur à l'index qui convertit 4 en 'brown'</span>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 16px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 0px; overflow: hidden; border: none; box-shadow: none; background: none; color: #307fc1;"><span style="box-sizing: border-box; border: none; padding: 0px; margin: 0px; box-shadow: none; background: none;"></span>[ ]:
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<div class="input_area highlight-ipython3 notranslate" style="box-sizing: border-box; margin: 0px; flex: 1 1 0%; overflow: auto; border: 1px solid #e0e0e0; border-radius: 2px;">
<div class="highlight" style="box-sizing: border-box; background: #f8f8f8; border: none; overflow: auto hidden; margin: 0px; padding: 0px; box-shadow: none;">
<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 16px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># 4.1.3 Copiez la définition de cmap et réexécutez-la pour ajouter la nouvelle couleur</span>
<span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># Affichez la zone</span>
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<p style="box-sizing: border-box; line-height: 24px; margin: 0px 0px 24px; font-size: 16px; text-align: left;"><strong style="box-sizing: border-box;">Astuce:</strong> Si vous voulez afficher la nouvelle zone, vous devez redéfinir <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">cmap</span></code> pour que la nouvelle valeur se voit attribuer une couleur dans la carte des couleurs. Copiez et collez la ligne <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">cmap</span> <span class="pre" style="box-sizing: border-box;">=</span> <span class="pre" style="box-sizing: border-box;">...</span></code> du tracé original.</p>
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<section id="4.2-Set-area[20:40,-80:95]-=-np.nan.-Plot-the-area-now." style="box-sizing: border-box;">
<h3 style="box-sizing: border-box; margin-top: 0px; font-weight: bold; font-size: 20px; color: #336699;">4.2 Définissez zone <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 15px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">area[20:40,</span> <span class="pre" style="box-sizing: border-box;">80:95]</span> <span class="pre" style="box-sizing: border-box;">=</span> <span class="pre" style="box-sizing: border-box;">np.nan</span></code>. Tracez la zone maintenant.<a class="headerlink" href="https://training.digitalearthafrica.org/en/latest/python_basics/04_cleaning_data.html#4.2-Set-area[20:40,-80:95]-=-np.nan.-Plot-the-area-now." title="Permalink to this headline" style="box-sizing: border-box; color: #2980b9; text-decoration-line: none; cursor: pointer; display: inline-block; font-variant-numeric: normal; font-variant-east-asian: normal; font-weight: normal; font-stretch: normal; line-height: 1; font-family: inherit; font-size: 14px; text-rendering: auto; -webkit-font-smoothing: antialiased; visibility: hidden;"></a></h3>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 16px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 0px; overflow: hidden; border: none; box-shadow: none; background: none; color: #307fc1;"><span style="box-sizing: border-box; border: none; padding: 0px; margin: 0px; box-shadow: none; background: none;"></span>[ ]:
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 16px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># Définissez la zone nan</span>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 16px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 0px; overflow: hidden; border: none; box-shadow: none; background: none; color: #307fc1;"><span style="box-sizing: border-box; border: none; padding: 0px; margin: 0px; box-shadow: none; background: none;"></span>[ ]:
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 16px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># Affichez toute la zone</span>
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<section id="4.3-Find-the-median-of-the-area-array-from-4.2-using-np.nanmedian.-Does-this-match-your-visual-interpretation?-How-does-this-compare-to-using-np.median?" style="box-sizing: border-box;">
<h3 style="box-sizing: border-box; margin-top: 0px; font-weight: bold; font-size: 20px; color: #336699; text-align: left;">4.3 Trouvez la médiane du tableau <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 15px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">area</span></code> de 4.2 en utilisant <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 15px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">np.nanmedian</span></code>. Est-ce que cela correspond à votre interprétation visuelle ? Comment cela se compare-t-il à l’utilisation de <code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 15px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">np.median</span></code>?<a class="headerlink" href="https://training.digitalearthafrica.org/en/latest/python_basics/04_cleaning_data.html#4.3-Find-the-median-of-the-area-array-from-4.2-using-np.nanmedian.-Does-this-match-your-visual-interpretation?-How-does-this-compare-to-using-np.median?" title="Permalink to this headline" style="box-sizing: border-box; color: #2980b9; text-decoration-line: none; cursor: pointer; display: inline-block; font-variant-numeric: normal; font-variant-east-asian: normal; font-weight: normal; font-stretch: normal; line-height: 1; font-family: inherit; font-size: 14px; text-rendering: auto; -webkit-font-smoothing: antialiased; visibility: hidden;"></a></h3>
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<pre style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 16px; white-space: pre; line-height: 1.4; margin-top: 0px; margin-bottom: 0px; padding: 5px; overflow: auto; border: none; box-shadow: none;"><span style="box-sizing: border-box;"></span><span class="c1" style="box-sizing: border-box; color: #408080; font-style: italic;"># Utilisez np.nanmedian pour trouver la médiane de la zone</span>
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<p style="text-align: left;">Deux capacités clés de Python ont été présentées dans cette section. Nous pouvons organiser nos données à l’aide de la syntaxe du dictionnaire, et comprendre les ensembles de données incomplets qui peuvent utiliser des valeurs<span> </span><code class="docutils literal notranslate" style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', Courier, monospace; font-size: 12px; white-space: nowrap; max-width: 100%; background-image: initial; background-color: #ffffff; border: 1px solid #e1e4e5; padding: 2px 5px; color: #e74c3c; overflow-x: auto;"><span class="pre" style="box-sizing: border-box;">NaN</span></code><span> </span>pour afficher les blancs. La leçon suivante fournit un guide sur xarray, un pacquet Python qui s’appuie sur ces concepts pour faciliter le chargement et l’utilisation des données multidimensionnelles.</p>
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