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<a href="decision__tree_2information__gain_8hpp.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno"> 1</span> </div><div class="line"><a name="l00013"></a><span class="lineno"> 13</span> <span class="preprocessor">#ifndef MLPACK_METHODS_DECISION_TREE_INFORMATION_GAIN_HPP</span></div><div class="line"><a name="l00014"></a><span class="lineno"> 14</span> <span class="preprocessor">#define MLPACK_METHODS_DECISION_TREE_INFORMATION_GAIN_HPP</span></div><div class="line"><a name="l00015"></a><span class="lineno"> 15</span> </div><div class="line"><a name="l00016"></a><span class="lineno"> 16</span> <span class="preprocessor">#include <<a class="code" href="prereqs_8hpp.html">mlpack/prereqs.hpp</a>></span></div><div class="line"><a name="l00017"></a><span class="lineno"> 17</span> </div><div class="line"><a name="l00018"></a><span class="lineno"> 18</span> <span class="keyword">namespace </span><a class="code" href="namespacemlpack.html">mlpack</a> {</div><div class="line"><a name="l00019"></a><span class="lineno"> 19</span> <span class="keyword">namespace </span>tree {</div><div class="line"><a name="l00020"></a><span class="lineno"> 20</span> </div><div class="line"><a name="l00025"></a><span class="lineno"><a class="line" href="classmlpack_1_1tree_1_1InformationGain.html"> 25</a></span> <span class="keyword">class </span><a class="code" href="classmlpack_1_1tree_1_1InformationGain.html">InformationGain</a></div><div class="line"><a name="l00026"></a><span class="lineno"> 26</span> {</div><div class="line"><a name="l00027"></a><span class="lineno"> 27</span>  <span class="keyword">public</span>:</div><div class="line"><a name="l00034"></a><span class="lineno"><a class="line" href="classmlpack_1_1tree_1_1InformationGain.html#ac50105cc9c959dc89754baa4ba9b6408"> 34</a></span>  <span class="keyword">static</span> <span class="keywordtype">double</span> <a class="code" href="classmlpack_1_1tree_1_1InformationGain.html#ac50105cc9c959dc89754baa4ba9b6408">Evaluate</a>(<span class="keyword">const</span> arma::Row<size_t>& labels,</div><div class="line"><a name="l00035"></a><span class="lineno"> 35</span>  <span class="keyword">const</span> <span class="keywordtype">size_t</span> numClasses)</div><div class="line"><a name="l00036"></a><span class="lineno"> 36</span>  {</div><div class="line"><a name="l00037"></a><span class="lineno"> 37</span>  <span class="comment">// Edge case: if there are no elements, the gain is zero.</span></div><div class="line"><a name="l00038"></a><span class="lineno"> 38</span>  <span class="keywordflow">if</span> (labels.n_elem == 0)</div><div class="line"><a name="l00039"></a><span class="lineno"> 39</span>  <span class="keywordflow">return</span> 0.0;</div><div class="line"><a name="l00040"></a><span class="lineno"> 40</span> </div><div class="line"><a name="l00041"></a><span class="lineno"> 41</span>  <span class="comment">// Count the number of elements in each class.</span></div><div class="line"><a name="l00042"></a><span class="lineno"> 42</span>  arma::Col<size_t> counts(numClasses);</div><div class="line"><a name="l00043"></a><span class="lineno"> 43</span>  counts.zeros();</div><div class="line"><a name="l00044"></a><span class="lineno"> 44</span>  <span class="keywordflow">for</span> (<span class="keywordtype">size_t</span> i = 0; i < labels.n_elem; ++i)</div><div class="line"><a name="l00045"></a><span class="lineno"> 45</span>  counts[labels[i]]++;</div><div class="line"><a name="l00046"></a><span class="lineno"> 46</span> </div><div class="line"><a name="l00047"></a><span class="lineno"> 47</span>  <span class="comment">// Calculate the information gain.</span></div><div class="line"><a name="l00048"></a><span class="lineno"> 48</span>  <span class="keywordtype">double</span> gain = 0.0;</div><div class="line"><a name="l00049"></a><span class="lineno"> 49</span>  <span class="keywordflow">for</span> (<span class="keywordtype">size_t</span> i = 0; i < numClasses; ++i)</div><div class="line"><a name="l00050"></a><span class="lineno"> 50</span>  {</div><div class="line"><a name="l00051"></a><span class="lineno"> 51</span>  <span class="keyword">const</span> <span class="keywordtype">double</span> f = ((double) counts[i] / (<span class="keywordtype">double</span>) labels.n_elem);</div><div class="line"><a name="l00052"></a><span class="lineno"> 52</span>  <span class="keywordflow">if</span> (f > 0.0)</div><div class="line"><a name="l00053"></a><span class="lineno"> 53</span>  gain += f * std::log2(f);</div><div class="line"><a name="l00054"></a><span class="lineno"> 54</span>  }</div><div class="line"><a name="l00055"></a><span class="lineno"> 55</span> </div><div class="line"><a name="l00056"></a><span class="lineno"> 56</span>  <span class="keywordflow">return</span> gain;</div><div class="line"><a name="l00057"></a><span class="lineno"> 57</span>  }</div><div class="line"><a name="l00058"></a><span class="lineno"> 58</span> </div><div class="line"><a name="l00066"></a><span class="lineno"><a class="line" href="classmlpack_1_1tree_1_1InformationGain.html#af18b0bba60c637ccbd5f4b60eb4b46b0"> 66</a></span>  <span class="keyword">static</span> <span class="keywordtype">double</span> <a class="code" href="classmlpack_1_1tree_1_1InformationGain.html#af18b0bba60c637ccbd5f4b60eb4b46b0">Range</a>(<span class="keyword">const</span> <span class="keywordtype">size_t</span> numClasses)</div><div class="line"><a name="l00067"></a><span class="lineno"> 67</span>  {</div><div class="line"><a name="l00068"></a><span class="lineno"> 68</span>  <span class="comment">// The best possible case gives an information gain of 0. The worst</span></div><div class="line"><a name="l00069"></a><span class="lineno"> 69</span>  <span class="comment">// possible case is even distribution, which gives n * (1/n * log2(1/n)) =</span></div><div class="line"><a name="l00070"></a><span class="lineno"> 70</span>  <span class="comment">// log2(1/n) = -log2(n). So, the range is log2(n).</span></div><div class="line"><a name="l00071"></a><span class="lineno"> 71</span>  <span class="keywordflow">return</span> std::log2(numClasses);</div><div class="line"><a name="l00072"></a><span class="lineno"> 72</span>  }</div><div class="line"><a name="l00073"></a><span class="lineno"> 73</span> };</div><div class="line"><a name="l00074"></a><span class="lineno"> 74</span> </div><div class="line"><a name="l00075"></a><span class="lineno"> 75</span> } <span class="comment">// namespace tree</span></div><div class="line"><a name="l00076"></a><span class="lineno"> 76</span> } <span class="comment">// namespace mlpack</span></div><div class="line"><a name="l00077"></a><span class="lineno"> 77</span> </div><div class="line"><a name="l00078"></a><span class="lineno"> 78</span> <span class="preprocessor">#endif</span></div><div class="ttc" id="namespacemlpack_html"><div class="ttname"><a href="namespacemlpack.html">mlpack</a></div><div class="ttdoc">Linear algebra utility functions, generally performed on matrices or vectors. </div><div class="ttdef"><b>Definition:</b> <a href="binarize_8hpp_source.html#l00018">binarize.hpp:18</a></div></div>
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<div class="ttc" id="classmlpack_1_1tree_1_1InformationGain_html_af18b0bba60c637ccbd5f4b60eb4b46b0"><div class="ttname"><a href="classmlpack_1_1tree_1_1InformationGain.html#af18b0bba60c637ccbd5f4b60eb4b46b0">mlpack::tree::InformationGain::Range</a></div><div class="ttdeci">static double Range(const size_t numClasses)</div><div class="ttdoc">Return the range of the information gain for the given number of classes. </div><div class="ttdef"><b>Definition:</b> <a href="decision__tree_2information__gain_8hpp_source.html#l00066">information_gain.hpp:66</a></div></div>
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<div class="ttc" id="prereqs_8hpp_html"><div class="ttname"><a href="prereqs_8hpp.html">prereqs.hpp</a></div><div class="ttdoc">The core includes that mlpack expects; standard C++ includes and Armadillo. </div></div>
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<div class="ttc" id="classmlpack_1_1tree_1_1InformationGain_html_ac50105cc9c959dc89754baa4ba9b6408"><div class="ttname"><a href="classmlpack_1_1tree_1_1InformationGain.html#ac50105cc9c959dc89754baa4ba9b6408">mlpack::tree::InformationGain::Evaluate</a></div><div class="ttdeci">static double Evaluate(const arma::Row< size_t > &labels, const size_t numClasses)</div><div class="ttdoc">Given a set of labels, calculate the information gain of those labels. </div><div class="ttdef"><b>Definition:</b> <a href="decision__tree_2information__gain_8hpp_source.html#l00034">information_gain.hpp:34</a></div></div>
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<div class="ttc" id="classmlpack_1_1tree_1_1InformationGain_html"><div class="ttname"><a href="classmlpack_1_1tree_1_1InformationGain.html">mlpack::tree::InformationGain</a></div><div class="ttdoc">The standard information gain criterion, used for calculating gain in decision trees. </div><div class="ttdef"><b>Definition:</b> <a href="decision__tree_2information__gain_8hpp_source.html#l00025">information_gain.hpp:25</a></div></div>
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