REF: use BlockManager.apply in csv code

pandas/core/internals/blocks.py

@@ -593,7 +593,7 @@ def astype(self, dtype, copy: bool = False, errors: str = "raise"):
 
                 # use native type formatting for datetime/tz/timedelta
                 if self.is_datelike:
-                    values = self.to_native_types()
+                    values = self.to_native_types().values
 
                 # astype formatting
                 else:
@@ -684,7 +684,7 @@ def to_native_types(self, na_rep="nan", quoting=None, **kwargs):
             values = np.array(values, dtype="object")
 
         values[mask] = na_rep
-        return values
+        return self.make_block(values)
 
     # block actions #
     def copy(self, deep: bool = True):
@@ -1774,7 +1774,7 @@ def to_native_types(self, na_rep="nan", quoting=None, **kwargs):
 
         # TODO(EA2D): reshape not needed with 2D EAs
         # we are expected to return a 2-d ndarray
-        return values.reshape(1, len(values))
+        return self.make_block(values)
 
     def take_nd(
         self, indexer, axis: int = 0, new_mgr_locs=None, fill_value=lib.no_default
@@ -2021,7 +2021,7 @@ def to_native_types(
                 values = np.array(values, dtype="object")
 
             values[mask] = na_rep
-            return values
+            return self.make_block(values)
 
         from pandas.io.formats.format import FloatArrayFormatter
 
@@ -2033,7 +2033,8 @@ def to_native_types(
             quoting=quoting,
             fixed_width=False,
         )
-        return formatter.get_result_as_array()
+        res = formatter.get_result_as_array()
+        return self.make_block(res)
 
 
 class ComplexBlock(FloatOrComplexBlock):
@@ -2192,7 +2193,7 @@ def to_native_types(self, na_rep="NaT", date_format=None, **kwargs):
         result = dta._format_native_types(
             na_rep=na_rep, date_format=date_format, **kwargs
         )
-        return np.atleast_2d(result)
+        return self.make_block(result)
 
     def set(self, locs, values):
         """
@@ -2408,7 +2409,8 @@ def fillna(self, value, **kwargs):
     def to_native_types(self, na_rep="NaT", **kwargs):
         """ convert to our native types format """
         tda = self.array_values()
-        return tda._format_native_types(na_rep, **kwargs)
+        res = tda._format_native_types(na_rep, **kwargs)
+        return self.make_block(res)
 
 
 class BoolBlock(NumericBlock):

pandas/io/formats/csvs.py

@@ -341,12 +341,11 @@ def _save_chunk(self, start_i: int, end_i: int) -> None:
         slicer = slice(start_i, end_i)
 
         df = self.obj.iloc[slicer]
+        mgr = df._mgr
 
-        for block in df._mgr.blocks:
-            d = block.to_native_types(**self._number_format)
-
-            for col_loc, col in zip(block.mgr_locs, d):
-                data[col_loc] = col
+        res = mgr.apply("to_native_types", **self._number_format)
+        for i in range(len(res.items)):
+            data[i] = res.iget_values(i)
 
         ix = self.data_index.to_native_types(slicer=slicer, **self._number_format)
         libwriters.write_csv_rows(data, ix, self.nlevels, self.cols, self.writer)