Implemented input check

machine_learning/multinomial_naive_bayes_classifier.py

@@ -11,7 +11,7 @@ from sklearn.datasets import fetch_20newsgroups
 from sklearn.metrics import accuracy_score
 
 
-def group_data_by_target(targets):
+def group_indices_by_target(targets):
     """
     Associates to each target label the indices of the examples with that label
 
@@ -22,21 +22,21 @@ def group_data_by_target(targets):
 
     Returns
     ----------
-    grouped_data : dict of (label : list)
-                   Maps each target label to the list of indices of the examples with that label
+    grouped_indices : dict of (label : list)
+                      Maps each target label to the list of indices of the examples with that label
 
     Example
     ----------
     >>> y = np.array([1, 2, 3, 1, 2, 5])
-    >>> group_data_by_target(y)
+    >>> group_indices_by_target(y)
     {1: [0, 3], 2: [1, 4], 3: [2], 5: [5]}
     """
-    grouped_data = {}
+    grouped_indices = {}
     for i, y in enumerate(targets):
-        if y not in grouped_data:
-            grouped_data[y] = []
-        grouped_data[y].append(i)
-    return grouped_data
+        if y not in grouped_indices:
+            grouped_indices[y] = []
+        grouped_indices[y].append(i)
+    return grouped_indices
 
 
 class MultinomialNBClassifier:
@@ -46,6 +46,16 @@ class MultinomialNBClassifier:
         self.priors = None
         self.alpha = alpha
 
+    def _check_X(self, X):
+        if not sparse.issparse(X):
+            raise ValueError("Matrix X must be an instance of scipy.sparse.csr_matrix")
+
+    def _check_X_y(self, X, y):
+        self._check_X(X)
+        if X.shape[0] != len(y):
+            raise ValueError(
+                "The expected dimension for array y is (" + str(X.shape[0]) + ",), but got (" + str(len(y)) + ",)")
+
     def fit(self, X, y):
         """
         Parameters
@@ -56,16 +66,15 @@ class MultinomialNBClassifier:
         y : array-like of shape (n_samples,)
             Target labels
         """
-        if not sparse.issparse(X):
-            raise ValueError("Matrix X must be an instance of scipy.sparse.csr_matrix")
+        self._check_X_y(X, y)
         n_examples, n_features = X.shape
-        grouped_data = group_data_by_target(y)
-        self.classes = list(grouped_data.keys())
+        grouped_indices = group_indices_by_target(y)
+        self.classes = list(grouped_indices.keys())
         self.priors = np.zeros(shape=len(self.classes))
         self.features_probs = np.zeros(shape=(len(self.classes), n_features))
 
         for i, class_i in enumerate(self.classes):
-            data_class_i = X[grouped_data[class_i]]
+            data_class_i = X[grouped_indices[class_i]]
             prior_class_i = data_class_i.shape[0] / n_examples
             self.priors[i] = prior_class_i
             tot_features_count = data_class_i.sum()   # count of all features in class_i
@@ -98,8 +107,7 @@ class MultinomialNBClassifier:
         >>> model.predict(X[2:3])
         array([3])
         """
-        if not sparse.issparse(X):
-            raise ValueError("Matrix X must be an instance of scipy.sparse.csr_matrix")
+        self._check_X(X)
         y_pred = []
         log_features_probs = np.log(self.features_probs)
         log_priors = np.log(self.priors)
@@ -126,7 +134,7 @@ def main():
     model.fit(X_train, y_train)
 
     y_pred = model.predict(X_test)
-    print("Accuracy of Naive Bayes text classifier: " + str(accuracy_score(y_test, y_pred)))
+    print("Accuracy of naive bayes text classifier: " + str(accuracy_score(y_test, y_pred)))
 
 
 if __name__ == "__main__":