From 01bcedde71e15333c91aebec5b36473aa2f2bd77 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Sat, 5 Sep 2020 15:54:54 -0700
Subject: [PATCH] REF: use BlockManager.apply in csv code

---
 pandas/core/internals/blocks.py | 16 +++++++++-------
 pandas/io/formats/csvs.py       | 25 +++++++++++--------------
 2 files changed, 20 insertions(+), 21 deletions(-)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 3bcd4debbf41a..3866d6d62ed9d 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -588,7 +588,7 @@ 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:
@@ -679,7 +679,7 @@ 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):
@@ -1769,7 +1769,7 @@ 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
@@ -2016,7 +2016,7 @@ 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
 
@@ -2028,7 +2028,8 @@ 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):
@@ -2187,7 +2188,7 @@ 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):
         """
@@ -2403,7 +2404,8 @@ 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):
diff --git a/pandas/io/formats/csvs.py b/pandas/io/formats/csvs.py
index 270caec022fef..ae0f692445279 100644
--- a/pandas/io/formats/csvs.py
+++ b/pandas/io/formats/csvs.py
@@ -326,21 +326,18 @@ def _save_chunk(self, start_i: int, end_i: int) -> None:
         slicer = slice(start_i, end_i)
 
         df = self.obj.iloc[slicer]
-        blocks = df._mgr.blocks
-
-        for i in range(len(blocks)):
-            b = blocks[i]
-            d = b.to_native_types(
-                na_rep=self.na_rep,
-                float_format=self.float_format,
-                decimal=self.decimal,
-                date_format=self.date_format,
-                quoting=self.quoting,
-            )
+        mgr = df._mgr
 
-            for col_loc, col in zip(b.mgr_locs, d):
-                # self.data is a preallocated list
-                self.data[col_loc] = col
+        res = mgr.apply(
+            "to_native_types",
+            na_rep=self.na_rep,
+            float_format=self.float_format,
+            decimal=self.decimal,
+            date_format=self.date_format,
+            quoting=self.quoting,
+        )
+        for i in range(len(res.items)):
+            self.data[i] = res.iget_values(i)
 
         ix = data_index.to_native_types(
             slicer=slicer,