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<a href="gini__impurity_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_HOEFFDING_TREES_GINI_INDEX_HPP</span></div><div class="line"><a name="l00014"></a><span class="lineno"> 14</span> <span class="preprocessor">#define MLPACK_METHODS_HOEFFDING_TREES_GINI_INDEX_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="l00021"></a><span class="lineno"><a class="line" href="classmlpack_1_1tree_1_1GiniImpurity.html"> 21</a></span> <span class="keyword">class </span><a class="code" href="classmlpack_1_1tree_1_1GiniImpurity.html">GiniImpurity</a></div><div class="line"><a name="l00022"></a><span class="lineno"> 22</span> {</div><div class="line"><a name="l00023"></a><span class="lineno"> 23</span>  <span class="keyword">public</span>:</div><div class="line"><a name="l00024"></a><span class="lineno"><a class="line" href="classmlpack_1_1tree_1_1GiniImpurity.html#ad4df1f1782283fc198b4eceaf5f7f110"> 24</a></span>  <span class="keyword">static</span> <span class="keywordtype">double</span> <a class="code" href="classmlpack_1_1tree_1_1GiniImpurity.html#ad4df1f1782283fc198b4eceaf5f7f110">Evaluate</a>(<span class="keyword">const</span> arma::Mat<size_t>& counts)</div><div class="line"><a name="l00025"></a><span class="lineno"> 25</span>  {</div><div class="line"><a name="l00026"></a><span class="lineno"> 26</span>  <span class="comment">// We need to sum over the difference between the un-split node and the</span></div><div class="line"><a name="l00027"></a><span class="lineno"> 27</span>  <span class="comment">// split nodes. First we'll calculate the number of elements in each split</span></div><div class="line"><a name="l00028"></a><span class="lineno"> 28</span>  <span class="comment">// and total.</span></div><div class="line"><a name="l00029"></a><span class="lineno"> 29</span>  <span class="keywordtype">size_t</span> numElem = 0;</div><div class="line"><a name="l00030"></a><span class="lineno"> 30</span>  arma::vec splitCounts(counts.n_cols);</div><div class="line"><a name="l00031"></a><span class="lineno"> 31</span>  <span class="keywordflow">for</span> (<span class="keywordtype">size_t</span> i = 0; i < counts.n_cols; ++i)</div><div class="line"><a name="l00032"></a><span class="lineno"> 32</span>  {</div><div class="line"><a name="l00033"></a><span class="lineno"> 33</span>  splitCounts[i] = arma::accu(counts.col(i));</div><div class="line"><a name="l00034"></a><span class="lineno"> 34</span>  numElem += splitCounts[i];</div><div class="line"><a name="l00035"></a><span class="lineno"> 35</span>  }</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">// Corner case: if there are no elements, the impurity is zero.</span></div><div class="line"><a name="l00038"></a><span class="lineno"> 38</span>  <span class="keywordflow">if</span> (numElem == 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>  arma::Col<size_t> classCounts = arma::sum(counts, 1);</div><div class="line"><a name="l00042"></a><span class="lineno"> 42</span> </div><div class="line"><a name="l00043"></a><span class="lineno"> 43</span>  <span class="comment">// Calculate the Gini impurity of the un-split node.</span></div><div class="line"><a name="l00044"></a><span class="lineno"> 44</span>  <span class="keywordtype">double</span> impurity = 0.0;</div><div class="line"><a name="l00045"></a><span class="lineno"> 45</span>  <span class="keywordflow">for</span> (<span class="keywordtype">size_t</span> i = 0; i < classCounts.n_elem; ++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="keyword">const</span> <span class="keywordtype">double</span> f = ((double) classCounts[i] / (<span class="keywordtype">double</span>) numElem);</div><div class="line"><a name="l00048"></a><span class="lineno"> 48</span>  impurity += f * (1.0 - f);</div><div class="line"><a name="l00049"></a><span class="lineno"> 49</span>  }</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="comment">// Now calculate the impurity of the split nodes and subtract them from the</span></div><div class="line"><a name="l00052"></a><span class="lineno"> 52</span>  <span class="comment">// overall impurity.</span></div><div class="line"><a name="l00053"></a><span class="lineno"> 53</span>  <span class="keywordflow">for</span> (<span class="keywordtype">size_t</span> i = 0; i < counts.n_cols; ++i)</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>  <span class="keywordflow">if</span> (splitCounts[i] > 0)</div><div class="line"><a name="l00056"></a><span class="lineno"> 56</span>  {</div><div class="line"><a name="l00057"></a><span class="lineno"> 57</span>  <span class="keywordtype">double</span> splitImpurity = 0.0;</div><div class="line"><a name="l00058"></a><span class="lineno"> 58</span>  <span class="keywordflow">for</span> (<span class="keywordtype">size_t</span> j = 0; j < counts.n_rows; ++j)</div><div class="line"><a name="l00059"></a><span class="lineno"> 59</span>  {</div><div class="line"><a name="l00060"></a><span class="lineno"> 60</span>  <span class="keyword">const</span> <span class="keywordtype">double</span> f = ((double) counts(j, i) / (double) splitCounts[i]);</div><div class="line"><a name="l00061"></a><span class="lineno"> 61</span>  splitImpurity += f * (1.0 - f);</div><div class="line"><a name="l00062"></a><span class="lineno"> 62</span>  }</div><div class="line"><a name="l00063"></a><span class="lineno"> 63</span> </div><div class="line"><a name="l00064"></a><span class="lineno"> 64</span>  impurity -= ((double) splitCounts[i] / (<span class="keywordtype">double</span>) numElem) *</div><div class="line"><a name="l00065"></a><span class="lineno"> 65</span>  splitImpurity;</div><div class="line"><a name="l00066"></a><span class="lineno"> 66</span>  }</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> </div><div class="line"><a name="l00069"></a><span class="lineno"> 69</span>  <span class="keywordflow">return</span> impurity;</div><div class="line"><a name="l00070"></a><span class="lineno"> 70</span>  }</div><div class="line"><a name="l00071"></a><span class="lineno"> 71</span> </div><div class="line"><a name="l00077"></a><span class="lineno"><a class="line" href="classmlpack_1_1tree_1_1GiniImpurity.html#ab2a220d3aabd5e5a5f53e7a1ae09437d"> 77</a></span>  <span class="keyword">static</span> <span class="keywordtype">double</span> <a class="code" href="classmlpack_1_1tree_1_1GiniImpurity.html#ab2a220d3aabd5e5a5f53e7a1ae09437d">Range</a>(<span class="keyword">const</span> <span class="keywordtype">size_t</span> numClasses)</div><div class="line"><a name="l00078"></a><span class="lineno"> 78</span>  {</div><div class="line"><a name="l00079"></a><span class="lineno"> 79</span>  <span class="comment">// The best possible case is that only one class exists, which gives a Gini</span></div><div class="line"><a name="l00080"></a><span class="lineno"> 80</span>  <span class="comment">// impurity of 0. The worst possible case is that the classes are evenly</span></div><div class="line"><a name="l00081"></a><span class="lineno"> 81</span>  <span class="comment">// distributed, which gives n * (1/n * (1 - 1/n)) = 1 - 1/n.</span></div><div class="line"><a name="l00082"></a><span class="lineno"> 82</span>  <span class="keywordflow">return</span> 1.0 - (1.0 / double(numClasses));</div><div class="line"><a name="l00083"></a><span class="lineno"> 83</span>  }</div><div class="line"><a name="l00084"></a><span class="lineno"> 84</span> };</div><div class="line"><a name="l00085"></a><span class="lineno"> 85</span> </div><div class="line"><a name="l00086"></a><span class="lineno"> 86</span> } <span class="comment">// namespace tree</span></div><div class="line"><a name="l00087"></a><span class="lineno"> 87</span> } <span class="comment">// namespace mlpack</span></div><div class="line"><a name="l00088"></a><span class="lineno"> 88</span> </div><div class="line"><a name="l00089"></a><span class="lineno"> 89</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="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_1GiniImpurity_html_ad4df1f1782283fc198b4eceaf5f7f110"><div class="ttname"><a href="classmlpack_1_1tree_1_1GiniImpurity.html#ad4df1f1782283fc198b4eceaf5f7f110">mlpack::tree::GiniImpurity::Evaluate</a></div><div class="ttdeci">static double Evaluate(const arma::Mat< size_t > &counts)</div><div class="ttdef"><b>Definition:</b> <a href="gini__impurity_8hpp_source.html#l00024">gini_impurity.hpp:24</a></div></div>
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<div class="ttc" id="classmlpack_1_1tree_1_1GiniImpurity_html_ab2a220d3aabd5e5a5f53e7a1ae09437d"><div class="ttname"><a href="classmlpack_1_1tree_1_1GiniImpurity.html#ab2a220d3aabd5e5a5f53e7a1ae09437d">mlpack::tree::GiniImpurity::Range</a></div><div class="ttdeci">static double Range(const size_t numClasses)</div><div class="ttdoc">Return the range of the Gini impurity for the given number of classes. </div><div class="ttdef"><b>Definition:</b> <a href="gini__impurity_8hpp_source.html#l00077">gini_impurity.hpp:77</a></div></div>
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<div class="ttc" id="classmlpack_1_1tree_1_1GiniImpurity_html"><div class="ttname"><a href="classmlpack_1_1tree_1_1GiniImpurity.html">mlpack::tree::GiniImpurity</a></div><div class="ttdef"><b>Definition:</b> <a href="gini__impurity_8hpp_source.html#l00021">gini_impurity.hpp:21</a></div></div>
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