in core/frame.py

changed method __getitem__ to use .mask directly (e.g. df.mask(df > 0) is equivalent semantically to df[df>0])

added inplace keyword to where method (to update the dataframe in place, default is NOT to use inplace, and return a new dataframe)

changed method _boolean_set_ to use where and inplace=True (this allows alignment of the passed values and is slightly less strict than the current method)

all tests pass (as well as an added test in boolean frame indexing)

Author: jreback

pandas/core/frame.py

@@ -1775,9 +1775,8 @@ def __getitem__(self, key):
         elif isinstance(self.columns, MultiIndex):
             return self._getitem_multilevel(key)
         elif isinstance(key, DataFrame):
-            values = key.values
-            if values.dtype == bool:
-                return self.values[values]
+            if key.values.dtype == bool:
+                return self.mask(key)
             else:
                 raise ValueError('Cannot index using non-boolean DataFrame')
         else:
@@ -1891,11 +1890,7 @@ def _boolean_set(self, key, value):
         if self._is_mixed_type:
             raise ValueError('Cannot do boolean setting on mixed-type frame')
 
-        if isinstance(value, DataFrame):
-            assert(value._indexed_same(self))
-            np.putmask(self.values, mask, value.values)
-        else:
-            self.values[mask] = value
+        self.where(key, value, inplace=True)
 
     def _set_item_multiple(self, keys, value):
         if isinstance(value, DataFrame):
@@ -4878,7 +4873,7 @@ def combineMult(self, other):
         """
         return self.mul(other, fill_value=1.)
 
-    def where(self, cond, other):
+    def where(self, cond, other, inplace=False):
         """
         Return a DataFrame with the same shape as self and whose corresponding
         entries are from self where cond is True and otherwise are from other.
@@ -4905,9 +4900,13 @@ def where(self, cond, other):
         if isinstance(other, DataFrame):
             _, other = self.align(other, join='left', fill_value=NA)
 
+        if inplace:
+            np.putmask(self.values, cond, other)
+            return self
+
         rs = np.where(cond, self, other)
         return self._constructor(rs, self.index, self.columns)
-
+        
     def mask(self, cond):
         """
         Returns copy of self whose values are replaced with nan if the

pandas/tests/test_frame.py

@@ -141,6 +141,12 @@ def test_getitem_boolean(self):
 
         self.assertRaises(ValueError, self.tsframe.__getitem__, self.tsframe)
 
+        # test df[df >0] works
+        bif = self.tsframe[self.tsframe > 0]
+        bifw = DataFrame(np.where(self.tsframe>0,self.tsframe,np.nan),index=self.tsframe.index,columns=self.tsframe.columns)
+        self.assert_(isinstance(bif,DataFrame))
+        self.assert_(bif.shape == self.tsframe.shape)
+        assert_frame_equal(bif,bifw)
 
     def test_getitem_boolean_list(self):
         df = DataFrame(np.arange(12).reshape(3,4))