Initial commit

Metrics.cpp

@@ -0,0 +1,65 @@
+#include "Metrics.h"
+#include <set>
+#include <cmath>
+using namespace std;
+namespace mdlp {
+    Metrics::Metrics(labels_t& y_, indices_t& indices_): y(y_), indices(indices_), numClasses(computeNumClasses(0, indices.size())), entropyCache(cacheEnt_t()), igCache(cacheIg_t())
+    {
+    }
+    int Metrics::computeNumClasses(size_t start, size_t end)
+    {
+        set<int> nClasses;
+        for (auto i = start; i < end; ++i) {
+            nClasses.insert(y[indices[i]]);
+        }
+        return nClasses.size();
+    }
+    void Metrics::setData(labels_t& y_, indices_t& indices_)
+    {
+        indices = indices_;
+        y = y_;
+        numClasses = computeNumClasses(0, indices.size());
+        entropyCache.clear();
+        igCache.clear();
+    }
+    precision_t Metrics::entropy(size_t start, size_t end)
+    {
+        precision_t p, ventropy = 0;
+        int nElements = 0;
+        labels_t counts(numClasses + 1, 0);
+        if (end - start < 2)
+            return 0;
+        if (entropyCache.find(make_tuple(start, end)) != entropyCache.end()) {
+            return entropyCache[make_tuple(start, end)];
+        }
+        for (auto i = &indices[start]; i != &indices[end]; ++i) {
+            counts[y[*i]]++;
+            nElements++;
+        }
+        for (auto count : counts) {
+            if (count > 0) {
+                p = (precision_t)count / nElements;
+                ventropy -= p * log2(p);
+            }
+        }
+        entropyCache[make_tuple(start, end)] = ventropy;
+        return ventropy;
+    }
+    precision_t Metrics::informationGain(size_t start, size_t cut, size_t end)
+    {
+        precision_t iGain;
+        precision_t entropyInterval, entropyLeft, entropyRight;
+        int nElementsLeft = cut - start, nElementsRight = end - cut;
+        int nElements = end - start;
+        if (igCache.find(make_tuple(start, cut, end)) != igCache.end()) {
+            return igCache[make_tuple(start, cut, end)];
+        }
+        entropyInterval = entropy(start, end);
+        entropyLeft = entropy(start, cut);
+        entropyRight = entropy(cut, end);
+        iGain = entropyInterval - ((precision_t)nElementsLeft * entropyLeft + (precision_t)nElementsRight * entropyRight) / nElements;
+        igCache[make_tuple(start, cut, end)] = iGain;
+        return iGain;
+    }
+
+}