Fix entropy and information gain

fimdlp/CPPFImdlp.cpp

@@ -18,14 +18,16 @@ namespace CPPFImdlp
     std::vector<float> CPPFImdlp::cutPoints(std::vector<float> &X, std::vector<int> &y)
     {
         std::vector<float> cutPts;
+        std::vector<int> cutIdx;
         float xPrev, cutPoint;
-        int yPrev;
+        int yPrev, idxPrev;
         std::vector<size_t> indices = sortIndices(X);
         xPrev = X.at(indices[0]);
         yPrev = y.at(indices[0]);
+        idxPrev = indices[0];
         if (debug)
         {
-            std::cout << "Entropy: " << Metrics::entropy(y, 0, y.size(), Metrics::numClasses(y)) << std::endl;
+            std::cout << "Entropy: " << Metrics::entropy(y, indices, 0, y.size(), Metrics::numClasses(y, indices, 0, indices.size())) << std::endl;
         }
         for (auto index = indices.begin(); index != indices.end(); ++index)
         {
@@ -37,12 +39,23 @@ namespace CPPFImdlp
                 {
                     std::cout << "Cut point: " << (xPrev + X.at(*index)) / 2 << " //";
                     std::cout << X.at(*index) << " -> " << y.at(*index) << " yPrev= " << yPrev;
-                    std::cout << "* (" << X.at(*index) << ", " << xPrev << ")=" << ((X.at(*index) + xPrev) / 2) << std::endl;
+                    std::cout << "* (" << X.at(*index) << ", " << xPrev << ")="
+                              << ((X.at(*index) + xPrev) / 2) << "idxPrev"
+                              << idxPrev << std::endl;
                 }
                 cutPts.push_back(cutPoint);
+                cutIdx.push_back(idxPrev);
             }
             xPrev = X.at(*index);
             yPrev = y.at(*index);
+            idxPrev = *index;
+        }
+        std::cout << "Information Gain:" << std::endl;
+        auto nc = Metrics::numClasses(y, indices, 0, indices.size());
+        for (auto cutPoint = cutIdx.begin(); cutPoint != cutIdx.end(); ++cutPoint)
+        {
+            std::cout << *cutPoint << " -> " << Metrics::informationGain(y, indices, 0, indices.size(), *cutPoint, nc) << std::endl;
+            //  << Metrics::informationGain(y, 0, y.size(), *cutPoint, Metrics::numClasses(y, 0, y.size())) << std::endl;
         }
         return cutPts;
     }

fimdlp/Metrics.cpp

@@ -4,15 +4,29 @@ namespace CPPFImdlp
     Metrics::Metrics()
     {
     }
-    float Metrics::entropy(std::vector<int> &y, int start, int end, int nClasses)
+    int Metrics::numClasses(std::vector<int> &y, std::vector<size_t> indices, int start, int end)
+    {
+        int nClasses = 1;
+        int yAnt = y.at(start);
+        for (auto i = start; i < end; ++i)
+        {
+            if (y.at(i) != yAnt)
+            {
+                nClasses++;
+                yAnt = y.at(i);
+            }
+        }
+        return nClasses;
+    }
+    float Metrics::entropy(std::vector<int> &y, std::vector<size_t> &indices, int start, int end, int nClasses)
     {
         float entropy = 0;
-        int nElements = end - start;
-        std::vector<int>
-            counts(nClasses, 0);
-        for (auto i = start; i < end; i++)
+        int nElements = 0;
+        std::vector<int> counts(nClasses, 0);
+        for (auto i = &indices[start]; i != &indices[end]; ++i)
         {
-            counts[y[i]]++;
+            counts[y[*i]]++;
+            nElements++;
         }
         for (auto i = 0; i < nClasses; i++)
         {
@@ -24,17 +38,20 @@ namespace CPPFImdlp
         }
         return entropy;
     }
-    int Metrics::numClasses(std::vector<int> &y)
+    float Metrics::informationGain(std::vector<int> &y, std::vector<size_t> &indices, int start, int end, int cutPoint, int nClasses)
     {
-        int nClasses = 1;
-        int yAnt = y.at(0);
-        for (auto i = y.begin(); i != y.end(); ++i)
-        {
-            if (*i != yAnt)
-            {
-                nClasses++;
-            }
-        }
-        return nClasses;
+        float iGain = 0.0;
+        float entropy, entropyLeft, entropyRight;
+        int nClassesLeft, nClassesRight;
+        int nElementsLeft = cutPoint - start, nElementsRight = end - cutPoint;
+        int nElements = end - start;
+        nClassesLeft = Metrics::numClasses(y, indices, start, cutPoint);
+        nClassesRight = Metrics::numClasses(y, indices, cutPoint, end);
+        entropy = Metrics::entropy(y, indices, start, end, nClasses);
+        entropyLeft = Metrics::entropy(y, indices, start, cutPoint, nClassesLeft);
+        entropyRight = Metrics::entropy(y, indices, cutPoint, end, nClassesRight);
+        iGain = entropy - (float)nElementsLeft / nElements * entropyLeft - (float)nElementsRight / nElements * entropyRight;
+        return iGain;
     }
+
 }

fimdlp/Metrics.h

@@ -9,8 +9,9 @@ namespace CPPFImdlp
     {
     public:
         Metrics();
-        static float entropy(std::vector<int> &, int, int, int);
-        static int numClasses(std::vector<int> &);
+        static int numClasses(std::vector<int> &, std::vector<size_t>, int, int);
+        static float entropy(std::vector<int> &, std::vector<size_t> &, int, int, int);
+        static float informationGain(std::vector<int> &y, std::vector<size_t> &indices, int start, int end, int cutPoint, int nClasses);
     };
 }
 #endif