Change entropy function with scipy (#38)

stree/Splitter.py

@@ -478,18 +478,6 @@ class Splitter:
 
     @staticmethod
     def _entropy(y: np.array) -> float:
-        """Compute entropy of a labels set
-
-        Parameters
-        ----------
-        y : np.array
-            set of labels
-
-        Returns
-        -------
-        float
-            entropy
-        """
         n_labels = len(y)
         if n_labels <= 1:
             return 0
@@ -497,13 +485,10 @@ class Splitter:
         proportions = counts / n_labels
         n_classes = np.count_nonzero(proportions)
         if n_classes <= 1:
-            return 0
-        entropy = 0.0
-        # Compute standard entropy.
-        for prop in proportions:
-            if prop != 0.0:
-                entropy -= prop * log(prop, n_classes)
-        return entropy
+            return 0.0
+        from scipy.stats import entropy
+
+        return entropy(y, base=n_classes)
 
     def information_gain(
         self, labels: np.array, labels_up: np.array, labels_dn: np.array