BUG: Fix issue with SparseArray

Author: hexgnu

pandas/core/internals.py

@@ -2756,6 +2756,11 @@ class SparseBlock(NonConsolidatableMixIn, Block):
     _holder = SparseArray
     _concatenator = staticmethod(_concat._concat_sparse)
 
+    def __init__(self, values, placement, ndim=None, fastpath=False, **kwargs):
+        super(SparseBlock, self).__init__(self._holder(values),
+                                            placement, ndim=ndim,
+                                                fastpath=fastpath, **kwargs)
+
     @property
     def shape(self):
         return (len(self.mgr_locs), self.sp_index.length)

pandas/core/reshape/reshape.py

@@ -841,10 +841,6 @@ def check_len(item, name):
             with_dummies = []
         else:
             with_dummies = [data.drop(columns_to_encode, axis=1)]
-            if sparse:
-                with_dummies = [SparseDataFrame(with_dummies[0],
-                                                index=with_dummies.index,
-                                                default_fill_value=0)]
 
         for (col, pre, sep) in zip(columns_to_encode, prefix, prefix_sep):
 

pandas/core/sparse/frame.py

@@ -14,7 +14,7 @@
 from pandas.core.dtypes.cast import maybe_upcast, find_common_type
 from pandas.core.dtypes.common import _ensure_platform_int, is_scipy_sparse
 
-from pandas.core.common import _try_sort
+from pandas.core.common import _try_sort, is_sparse
 from pandas.compat.numpy import function as nv
 from pandas.core.index import Index, MultiIndex, _ensure_index
 from pandas.core.series import Series
@@ -306,7 +306,7 @@ def to_dense(self):
         -------
         df : DataFrame
         """
-        data = {k: v.to_dense() for k, v in compat.iteritems(self)}
+        data = {k: v.to_dense() if is_sparse(v) else v for k, v in compat.iteritems(self)}
         return DataFrame(data, index=self.index, columns=self.columns)
 
     def _apply_columns(self, func):

pandas/tests/sparse/test_array.py

@@ -465,7 +465,7 @@ def test_to_dense(self):
         with tm.assert_produces_warning(FutureWarning,
                                         check_stacklevel=False):
             SparseArray(vals).to_dense(fill=2)
-
+    
     def test_getitem(self):
         def _checkit(i):
             assert_almost_equal(self.arr[i], self.arr.values[i])

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
+from pandas import Series, DataFrame, bdate_range, Panel, get_dummies
 from pandas.core.dtypes.common import (
     is_bool_dtype,
     is_float_dtype,
@@ -323,7 +323,13 @@ def test_density(self):
         assert df.density == 0.75
 
     def test_sparse_to_dense(self):
-        pass
+        # 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)