BUG: Add copy parameter to prevent reinterpret cast of sparse

Author: Licht-T

pandas/core/internals.py

@@ -988,7 +988,7 @@ def f(m, v, i):
 
         return [self.make_block(new_values, fastpath=True)]
 
-    def coerce_to_target_dtype(self, other):
+    def coerce_to_target_dtype(self, other, copy=False):
         """
         coerce the current block to a dtype compat for other
         we will return a block, possibly object, and not raise
@@ -1005,7 +1005,7 @@ def coerce_to_target_dtype(self, other):
 
         if self.is_bool or is_object_dtype(dtype) or is_bool_dtype(dtype):
             # we don't upcast to bool
-            return self.astype(object)
+            return self.astype(object, copy=copy)
 
         elif ((self.is_float or self.is_complex) and
               (is_integer_dtype(dtype) or is_float_dtype(dtype))):
@@ -1019,14 +1019,14 @@ def coerce_to_target_dtype(self, other):
             # not a datetime
             if not ((is_datetime64_dtype(dtype) or
                      is_datetime64tz_dtype(dtype)) and self.is_datetime):
-                return self.astype(object)
+                return self.astype(object, copy=copy)
 
             # don't upcast timezone with different timezone or no timezone
             mytz = getattr(self.dtype, 'tz', None)
             othertz = getattr(dtype, 'tz', None)
 
             if str(mytz) != str(othertz):
-                return self.astype(object)
+                return self.astype(object, copy=copy)
 
             raise AssertionError("possible recursion in "
                                  "coerce_to_target_dtype: {} {}".format(
@@ -1036,18 +1036,18 @@ def coerce_to_target_dtype(self, other):
 
             # not a timedelta
             if not (is_timedelta64_dtype(dtype) and self.is_timedelta):
-                return self.astype(object)
+                return self.astype(object, copy=copy)
 
             raise AssertionError("possible recursion in "
                                  "coerce_to_target_dtype: {} {}".format(
                                      self, other))
 
         try:
-            return self.astype(dtype)
+            return self.astype(dtype, copy=copy)
         except (ValueError, TypeError):
             pass
 
-        return self.astype(object)
+        return self.astype(object, copy=copy)
 
     def interpolate(self, method='pad', axis=0, index=None, values=None,
                     inplace=False, limit=None, limit_direction='forward',
@@ -2636,6 +2636,9 @@ class SparseBlock(NonConsolidatableMixIn, Block):
     _ftype = 'sparse'
     _holder = SparseArray
 
+    def coerce_to_target_dtype(self, other, copy=True):
+        return super(SparseBlock, self).coerce_to_target_dtype(other, copy)
+
     @property
     def shape(self):
         return (len(self.mgr_locs), self.sp_index.length)

pandas/core/sparse/array.py

@@ -248,7 +248,7 @@ def _simple_new(cls, data, sp_index, fill_value):
                 sp_index.ngaps > 0):
             # if float fill_value is being included in dense repr,
             # convert values to float
-            data = data.astype(float)
+            data = data.astype(float, copy=True)
 
         result = data.view(cls)