trees.py 文件源码

def entropy(self, targets):
        """
        Returns the entropy in the given rows.
        :param targets:     1D array-like targets
        :return:            Float value of entropy
        """
        results = self.unique_counts(targets)
        ent = 0.0
        for val in results.values():
            p = float(val) / len(targets)
            ent -= p * log2(p)
        return ent