PERF: get_dummies return bool columns

Make get_dummies() return columns of dtype=bool instead of np.float64
BUG: dtype compat with get_dummies pandas-dev#8725
pandas-dev#8725

Since all the point of this method is to return binary features there's no point to waste RAM and represent them using floats

Author: avishaylivne

pandas/core/reshape.py

@@ -1163,10 +1163,10 @@ def get_empty_Frame(data, sparse):
                                sparse_index=IntIndex(N, ixs), fill_value=0)
             sparse_series[col] = SparseSeries(data=sarr, index=index)
 
-        return SparseDataFrame(sparse_series, index=index, columns=dummy_cols)
+        return SparseDataFrame(sparse_series, index=index, columns=dummy_cols, dtype=bool)
 
     else:
-        dummy_mat = np.eye(number_of_cols).take(codes, axis=0)
+        dummy_mat = np.eye(number_of_cols, dtype=bool).take(codes, axis=0)
 
         if not dummy_na:
             # reset NaN GH4446
@@ -1176,7 +1176,7 @@ def get_empty_Frame(data, sparse):
             # remove first GH12042
             dummy_mat = dummy_mat[:, 1:]
             dummy_cols = dummy_cols[1:]
-        return DataFrame(dummy_mat, index=index, columns=dummy_cols)
+        return DataFrame(dummy_mat, index=index, columns=dummy_cols, dtype=bool)
 
 
 def make_axis_dummies(frame, axis='minor', transform=None):