PERF: frame: avoid unnecessary .values calls

Besides hstacking cols (data copy), this densifies SparseDataFrame.

Author: kernc

pandas/core/frame.py

@@ -734,11 +734,9 @@ def iterrows(self):
         iteritems : Iterate over (column name, Series) pairs.
 
         """
-        columns = self.columns
-        klass = self._constructor_sliced
-        for k, v in zip(self.index, self.values):
-            s = klass(v, index=columns, name=k)
-            yield k, s
+        iloc = self.iloc
+        for i, k in enumerate(self.index):
+            yield k, iloc[i]
 
     def itertuples(self, index=True, name="Pandas"):
         """
@@ -2186,7 +2184,7 @@ def _getitem_multilevel(self, key):
             return self._get_item_cache(key)
 
     def _getitem_frame(self, key):
-        if key.values.size and not is_bool_dtype(key.values):
+        if key.size and not key.dtypes.map(is_bool_dtype).all():
             raise ValueError('Must pass DataFrame with boolean values only')
         return self.where(key)
 
@@ -2518,7 +2516,7 @@ def _setitem_array(self, key, value):
     def _setitem_frame(self, key, value):
         # support boolean setting with DataFrame input, e.g.
         # df[df > df2] = 0
-        if key.values.size and not is_bool_dtype(key.values):
+        if key.size and not key.dtypes.map(is_bool_dtype).all():
             raise TypeError('Must pass DataFrame with boolean values only')
 
         self._check_inplace_setting(value)