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<!-- navigation toc: --> <li><a href="._week44-bs001.html#overview-of-week-44" style="font-size: 80%;">Overview of week 44</a></li>
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<!-- navigation toc: --> <li><a href="._week44-bs007.html#thursday-clustering-and-unsupervised-learning" style="font-size: 80%;">Thursday: Clustering and Unsupervised Learning</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs008.html#basic-idea-of-the-k-means-clustering-algorithm" style="font-size: 80%;">Basic Idea of the \( k \)-means Clustering Algorithm</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs009.html#the-k-means-algorithm" style="font-size: 80%;">The \( k \)-means Algorithm</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs010.html#basic-math-of-the-k-means-algorithm" style="font-size: 80%;">Basic Math of the \( k \)-means Algorithm</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs011.html#within-cluster-point-scatter" style="font-size: 80%;">Within Cluster Point Scatter</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs012.html#more-details" style="font-size: 80%;">More Details</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs013.html#total-cluster-variance" style="font-size: 80%;">Total Cluster Variance</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs014.html#the-k-means-clustering-algorithm" style="font-size: 80%;">The \( k \)-means Clustering Algorithm</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs015.html#summarizing" style="font-size: 80%;">Summarizing</a></li>
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<!-- navigation toc: --> <li><a href="._week44-bs017.html#implementing-the-k-means-algorithm" style="font-size: 80%;">Implementing the \( k \)-means Algorithm</a></li>
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<!-- navigation toc: --> <li><a href="._week44-bs020.html#wrapping-it-up" style="font-size: 80%;">Wrapping it up</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs021.html#decision-trees-overarching-aims" style="font-size: 80%;">Decision trees, overarching aims</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs022.html#basics-of-a-tree" style="font-size: 80%;">Basics of a tree</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs023.html#a-sketch-of-a-tree-regression-problem" style="font-size: 80%;">A Sketch of a Tree, Regression problem</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs024.html#a-sketch-of-a-tree-classification-problem" style="font-size: 80%;">A Sketch of a Tree, Classification problem</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs025.html#a-typical-decision-tree-with-its-pertinent-jargon-classification-problem" style="font-size: 80%;">A typical Decision Tree with its pertinent Jargon, Classification Problem</a></li>
<!-- navigation toc: --> <li><a href="#general-features" style="font-size: 80%;">General Features</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs027.html#how-do-we-set-it-up" style="font-size: 80%;">How do we set it up?</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs028.html#decision-trees-and-regression" style="font-size: 80%;">Decision trees and Regression</a></li>
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<!-- navigation toc: --> <li><a href="._week44-bs030.html#a-top-down-approach-recursive-binary-splitting" style="font-size: 80%;">A top-down approach, recursive binary splitting</a></li>
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<!-- navigation toc: --> <li><a href="._week44-bs039.html#visualizing-the-tree-the-moons" style="font-size: 80%;">Visualizing the Tree, The Moons</a></li>
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<!-- navigation toc: --> <li><a href="._week44-bs042.html#algorithms-for-setting-up-decision-trees" style="font-size: 80%;">Algorithms for Setting up Decision Trees</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs043.html#the-cart-algorithm-for-classification" style="font-size: 80%;">The CART algorithm for Classification</a></li>
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<!-- navigation toc: --> <li><a href="._week44-bs046.html#simple-python-code-to-read-in-data-and-perform-classification" style="font-size: 80%;">Simple Python Code to read in Data and perform Classification</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs047.html#computing-the-gini-factor" style="font-size: 80%;">Computing the Gini Factor</a></li>
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<!-- navigation toc: --> <li><a href="._week44-bs049.html#cancer-data-again-now-with-decision-trees-and-other-methods" style="font-size: 80%;">Cancer Data again now with Decision Trees and other Methods</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs050.html#another-example-the-moons-again" style="font-size: 80%;">Another example, the moons again</a></li>
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<!-- navigation toc: --> <li><a href="._week44-bs052.html#regression-trees" style="font-size: 80%;">Regression trees</a></li>
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<!-- navigation toc: --> <li><a href="._week44-bs054.html#pros-and-cons-of-trees-pros" style="font-size: 80%;">Pros and cons of trees, pros</a></li>
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<!-- navigation toc: --> <li><a href="._week44-bs056.html#ensemble-methods-from-a-single-tree-to-many-trees-and-extreme-boosting-meet-the-jungle-of-methods" style="font-size: 80%;">Ensemble Methods: From a Single Tree to Many Trees and Extreme Boosting, Meet the Jungle of Methods</a></li>
<!-- navigation toc: --> <li><a href="._week44-bs057.html#an-overview-of-ensemble-methods" style="font-size: 80%;">An Overview of Ensemble Methods</a></li>
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<h2 id="general-features" class="anchor">General Features </h2>
<p>The overarching approach to decision trees is a top-down approach.</p>
<ul>
<li> A leaf provides the classification of a given instance.</li>
<li> A node specifies a test of some attribute of the instance.</li>
<li> A branch corresponds to a possible values of an attribute.</li>
<li> An instance is classified by starting at the root node of the tree, testing the attribute specified by this node, then moving down the tree branch corresponding to the value of the attribute in the given example.</li>
</ul>
<p>This process is then repeated for the subtree rooted at the new
node.
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