Merge pull request #79 from Shihab-Shahriar/master

Fixed a bug in decision tree's _calculate_leaf_value method

Author: rushter

examples/random_forest.py

@@ -1,8 +1,9 @@
 import logging
 
+import numpy as np
 from sklearn.datasets import make_classification
 from sklearn.datasets import make_regression
-from sklearn.metrics import roc_auc_score
+from sklearn.metrics import roc_auc_score, accuracy_score
 
 try:
     from sklearn.model_selection import train_test_split
@@ -25,9 +26,12 @@ def classification():
 
     model = RandomForestClassifier(n_estimators=10, max_depth=4)
     model.fit(X_train, y_train)
-    predictions = model.predict(X_test)[:, 1]
-    # print(predictions)
-    print("classification, roc auc score: %s" % roc_auc_score(y_test, predictions))
+
+    predictions_prob = model.predict(X_test)[:, 1]
+    predictions = np.argmax(model.predict(X_test), axis=1)
+    #print(predictions.shape)
+    print("classification, roc auc score: %s" % roc_auc_score(y_test, predictions_prob))
+    print("classification, accuracy score: %s" % accuracy_score(y_test, predictions))
 
 
 def regression():

mla/ensemble/random_forest.py

@@ -44,7 +44,7 @@ def _train(self):
                 self.y,
                 max_features=self.max_features,
                 min_samples_split=self.min_samples_split,
-                max_depth=self.max_depth,
+                max_depth=self.max_depth
             )
 
     def _predict(self, X=None):

mla/ensemble/tree.py

@@ -12,14 +12,15 @@
 class Tree(object):
     """Recursive implementation of decision tree."""
 
-    def __init__(self, regression=False, criterion=None):
+    def __init__(self, regression=False, criterion=None, n_classes=None):
         self.regression = regression
         self.impurity = None
         self.threshold = None
         self.column_index = None
         self.outcome = None
         self.criterion = criterion
         self.loss = None
+        self.n_classes = n_classes  # Only for classification
 
         self.left_child = None
         self.right_child = None
@@ -64,6 +65,42 @@ def _find_best_split(self, X, target, n_features):
                     max_col, max_val, max_gain = column, value, gain
         return max_col, max_val, max_gain
 
+    def _train(self, X, target, max_features=None, min_samples_split=10, max_depth=None, minimum_gain=0.01):
+        try:
+            # Exit from recursion using assert syntax
+            assert X.shape[0] > min_samples_split
+            assert max_depth > 0
+
+            if max_features is None:
+                max_features = X.shape[1]
+
+            column, value, gain = self._find_best_split(X, target, max_features)
+            assert gain is not None
+            if self.regression:
+                assert gain != 0
+            else:
+                assert gain > minimum_gain
+
+            self.column_index = column
+            self.threshold = value
+            self.impurity = gain
+
+            # Split dataset
+            left_X, right_X, left_target, right_target = split_dataset(X, target, column, value)
+
+            # Grow left and right child
+            self.left_child = Tree(self.regression, self.criterion, self.n_classes)
+            self.left_child._train(
+                left_X, left_target, max_features, min_samples_split, max_depth - 1, minimum_gain
+            )
+
+            self.right_child = Tree(self.regression, self.criterion, self.n_classes)
+            self.right_child._train(
+                right_X, right_target, max_features, min_samples_split, max_depth - 1, minimum_gain
+            )
+        except AssertionError:
+            self._calculate_leaf_value(target)
+
     def train(self, X, target, max_features=None, min_samples_split=10, max_depth=None, minimum_gain=0.01, loss=None):
         """Build a decision tree from training set.
 
@@ -93,40 +130,12 @@ def train(self, X, target, max_features=None, min_samples_split=10, max_depth=No
         if loss is not None:
             self.loss = loss
 
-        try:
-            # Exit from recursion using assert syntax
-            assert X.shape[0] > min_samples_split
-            assert max_depth > 0
-
-            if max_features is None:
-                max_features = X.shape[1]
+        if not self.regression:
+            self.n_classes = len(np.unique(target['y']))
 
-            column, value, gain = self._find_best_split(X, target, max_features)
-            assert gain is not None
-            if self.regression:
-                assert gain != 0
-            else:
-                assert gain > minimum_gain
+        self._train(X, target, max_features=max_features, min_samples_split=min_samples_split,
+                    max_depth=max_depth, minimum_gain=minimum_gain)
 
-            self.column_index = column
-            self.threshold = value
-            self.impurity = gain
-
-            # Split dataset
-            left_X, right_X, left_target, right_target = split_dataset(X, target, column, value)
-
-            # Grow left and right child
-            self.left_child = Tree(self.regression, self.criterion)
-            self.left_child.train(
-                left_X, left_target, max_features, min_samples_split, max_depth - 1, minimum_gain, loss
-            )
-
-            self.right_child = Tree(self.regression, self.criterion)
-            self.right_child.train(
-                right_X, right_target, max_features, min_samples_split, max_depth - 1, minimum_gain, loss
-            )
-        except AssertionError:
-            self._calculate_leaf_value(target)
 
     def _calculate_leaf_value(self, targets):
         """Find optimal value for leaf."""
@@ -140,7 +149,7 @@ def _calculate_leaf_value(self, targets):
                 self.outcome = np.mean(targets["y"])
             else:
                 # Probability for classification task
-                self.outcome = stats.itemfreq(targets["y"])[:, 1] / float(targets["y"].shape[0])
+                self.outcome = np.bincount(targets["y"], minlength=self.n_classes) / targets["y"].shape[0]
 
     def predict_row(self, row):
         """Predict single row."""