Moved example notebook, and expanded numpy_div0 to div_safe

tests/test_utils.py

@@ -326,6 +326,32 @@ def test_classifier_visualizer(self):
         model = ScoreVisualizer(RandomForestClassifier())
         self.assertTrue(is_classifier(model))
 
+
+class DivSafeTests(unittest.TestCase):
+
+    def test_div_1d_by_scalar(self):
+        result = div_safe( [-1, 0, 1], 0 )
+        self.assertTrue(result.all() == 0)
+
+    def test_div_1d_by_1d(self):
+        result =div_safe( [-1, 0 , 1], [0,0,0])
+        self.assertTrue(result.all() == 0)
+
+    def test_div_2d_by_1d(self):
+        numerator = np.array([[-1,0,1,2],[1,-1,0,3]])
+        denominator = [0,0,0,0]
+        result = div_safe(numerator, denominator)
+
+    def test_invalid_dimensions(self):
+            numerator = np.array([[-1,0,1,2],[1,-1,0,3]])
+            denominator = [0,0]
+            with self.assertRaises(ValueError):
+                result = div_safe(numerator, denominator)
+
+    def test_div_scalar_by_scalar(self):
+        with self.assertRaises(ValueError):
+            result = div_safe(5, 0)
+
 ##########################################################################
 ## Decorator Tests
 ##########################################################################

yellowbrick/classifier.py

@@ -32,7 +32,7 @@
 from .base import Visualizer, ScoreVisualizer, MultiModelMixin
 from .style.palettes import color_sequence, color_palette, LINE_COLOR
 
-from .utils import numpy_div0
+from .utils import div_safe
 
 
 ##########################################################################
@@ -202,8 +202,8 @@ def draw(self, percent=True):
 
         if percent == True:
             #Convert confusion matrix to percent of each row, i.e. the predicted as a percent of true in each class
-            #numpy_div0 function returns 0 instead of NAN.
-            self._confusion_matrix_display = numpy_div0(
+            #div_safe function returns 0 instead of NAN.
+            self._confusion_matrix_display = div_safe(
                     self.confusion_matrix,
                     self.selected_class_counts
                     )

yellowbrick/utils.py

@@ -157,15 +157,32 @@ def is_dataframe(obj):
 
 
 #From here: http://stackoverflow.com/questions/26248654/numpy-return-0-with-divide-by-zero
-def numpy_div0( a, b ):
+def div_safe( numerator, denominator ):
     """
     Ufunc-extension that returns 0 instead of nan when dividing numpy arrays
-    example: >> div0( [-1, 0, 1], 0 ) -> [0, 0, 0]
+    
+    Parameters
+    ----------
+    numerator: array-like 
+
+    denominator: scalar or array-like that can be validly divided by the numerator
+
+    returns a numpy array
+
+    example: div_safe( [-1, 0, 1], 0 ) == [0, 0, 0]
     """
-    with np.errstate(divide='ignore', invalid='ignore'):
-        c = np.true_divide( a, b )
-        c[ ~ np.isfinite( c )] = 0  # -inf inf NaN
-    return c
+    #First handle scalars
+    if np.isscalar(numerator):
+        raise ValueError("div_safe should only be used with an array-like numerator")
+
+    #Then numpy arrays
+    try:
+        with np.errstate(divide='ignore', invalid='ignore'):
+            result = np.true_divide( numerator, denominator )
+            result[ ~ np.isfinite( result )] = 0  # -inf inf NaN
+        return result
+    except ValueError as e:
+        raise e
 
 ##########################################################################
 ## Decorators