BUG: SparseDataFrame iff all are sparse

Author: hexgnu

pandas/core/dtypes/concat.py

@@ -92,7 +92,7 @@ def _get_frame_result_type(result, objs):
     if any block is SparseBlock, return SparseDataFrame
     otherwise, return 1st obj
     """
-    if any(b.is_sparse for b in result.blocks):
+    if all(b.is_sparse for b in result.blocks):
         from pandas.core.sparse.api import SparseDataFrame
         return SparseDataFrame
     else:

pandas/core/sparse/frame.py

@@ -306,7 +306,7 @@ def to_dense(self):
         -------
         df : DataFrame
         """
-        data = {k: v.to_dense() if is_sparse(v) else v for k, v in compat.iteritems(self)}
+        data = {k: v.to_dense() for k, v in compat.iteritems(self)}
         return DataFrame(data, index=self.index, columns=self.columns)
 
     def _apply_columns(self, func):

pandas/core/sparse/series.py

@@ -168,7 +168,6 @@ def __init__(self, data=None, index=None, sparse_index=None, kind='block',
                 if index is None:
                     index = data.index.view()
                 else:
-
                     data = data.reindex(index, copy=False)
 
             else:

pandas/tests/sparse/test_frame.py

@@ -9,7 +9,7 @@
 import pandas as pd
 from distutils.version import LooseVersion
 
-from pandas import Series, DataFrame, bdate_range, Panel, get_dummies
+from pandas import Series, DataFrame, bdate_range, Panel
 from pandas.core.dtypes.common import (
     is_bool_dtype,
     is_float_dtype,
@@ -322,15 +322,6 @@ def test_density(self):
 
         assert df.density == 0.75
 
-    def test_sparse_to_dense(self):
-        # See gh-
-        sdf = DataFrame.from_items([('GDP', [1, 2]),('Nation', ['AB', 'CD'])])
-        sdf = get_dummies(sdf, columns=['Nation'], sparse=True)
-        df = sdf.to_dense()
-
-        tm.assert_frame_equals(df, sdf)
-
-
     def test_sparse_series_ops(self):
         self._check_frame_ops(self.frame)