REF: remove Block.concat_same_type (pandas-dev#33486)

Author: jbrockmendel

pandas/core/internals/blocks.py

@@ -48,7 +48,6 @@
  is_timedelta64_dtype,
  pandas_dtype,
 )
-from pandas.core.dtypes.concat import concat_categorical, concat_datetime
 from pandas.core.dtypes.dtypes import ExtensionDtype
 from pandas.core.dtypes.generic import (
  ABCDataFrame,
@@ -110,7 +109,6 @@ class Block(PandasObject):
  _can_consolidate = True
  _verify_integrity = True
  _validate_ndim = True
- _concatenator = staticmethod(np.concatenate)
 
  def __init__(self, values, placement, ndim=None):
  self.ndim = self._check_ndim(values, ndim)
@@ -309,16 +307,6 @@ def shape(self):
  def dtype(self):
  return self.values.dtype
 
- def concat_same_type(self, to_concat):
- """
- Concatenate list of single blocks of the same type.
- """
- values = self._concatenator(
- [blk.values for blk in to_concat], axis=self.ndim - 1
- )
- placement = self.mgr_locs if self.ndim == 2 else slice(len(values))
- return self.make_block_same_class(values, placement=placement)
-
  def iget(self, i):
  return self.values[i]
 
@@ -1770,14 +1758,6 @@ def _slice(self, slicer):
 
  return self.values[slicer]
 
- def concat_same_type(self, to_concat):
- """
- Concatenate list of single blocks of the same type.
- """
- values = self._holder._concat_same_type([blk.values for blk in to_concat])
- placement = self.mgr_locs if self.ndim == 2 else slice(len(values))
- return self.make_block_same_class(values, placement=placement)
-
  def fillna(self, value, limit=None, inplace=False, downcast=None):
  values = self.values if inplace else self.values.copy()
  values = values.fillna(value=value, limit=limit)
@@ -2258,20 +2238,6 @@ def diff(self, n: int, axis: int = 0) -> List["Block"]:
  new_values = new_values.astype("timedelta64[ns]")
  return [TimeDeltaBlock(new_values, placement=self.mgr_locs.indexer)]
 
- def concat_same_type(self, to_concat):
- # need to handle concat([tz1, tz2]) here, since DatetimeArray
- # only handles cases where all the tzs are the same.
- # Instead of placing the condition here, it could also go into the
- # is_uniform_join_units check, but I'm not sure what is better.
- if len({x.dtype for x in to_concat}) > 1:
- values = concat_datetime([x.values for x in to_concat])
-
- values = values.astype(object, copy=False)
- placement = self.mgr_locs if self.ndim == 2 else slice(len(values))
-
- return self.make_block(values, placement=placement)
- return super().concat_same_type(to_concat)
-
  def fillna(self, value, limit=None, inplace=False, downcast=None):
  # We support filling a DatetimeTZ with a `value` whose timezone
  # is different by coercing to object.
@@ -2642,7 +2608,6 @@ class CategoricalBlock(ExtensionBlock):
  is_categorical = True
  _verify_integrity = True
  _can_hold_na = True
- _concatenator = staticmethod(concat_categorical)
 
  should_store = Block.should_store
 
@@ -2656,26 +2621,6 @@ def __init__(self, values, placement, ndim=None):
  def _holder(self):
  return Categorical
 
- def concat_same_type(self, to_concat):
- """
- Concatenate list of single blocks of the same type.
-
- Note that this CategoricalBlock._concat_same_type *may* not
- return a CategoricalBlock. When the categories in `to_concat`
- differ, this will return an object ndarray.
-
- If / when we decide we don't like that behavior:
-
- 1. Change Categorical._concat_same_type to use union_categoricals
- 2. Delete this method.
- """
- values = self._concatenator(
- [blk.values for blk in to_concat], axis=self.ndim - 1
- )
- placement = self.mgr_locs if self.ndim == 2 else slice(len(values))
- # not using self.make_block_same_class as values can be object dtype
- return self.make_block(values, placement=placement)
-
  def replace(
  self,
  to_replace,

pandas/core/internals/concat.py

@@ -1,6 +1,7 @@
 # TODO: Needs a better name; too many modules are already called "concat"
 from collections import defaultdict
 import copy
+from typing import List
 
 import numpy as np
 
@@ -61,8 +62,18 @@ def concatenate_block_managers(
  values = values.view()
  b = b.make_block_same_class(values, placement=placement)
  elif _is_uniform_join_units(join_units):
- b = join_units[0].block.concat_same_type([ju.block for ju in join_units])
- b.mgr_locs = placement
+ blk = join_units[0].block
+ vals = [ju.block.values for ju in join_units]
+
+ if not blk.is_extension or blk.is_datetimetz or blk.is_categorical:
+ # datetimetz and categorical can have the same type but multiple
+ # dtypes, concatting does not necessarily preserve dtype
+ values = concat_compat(vals, axis=blk.ndim - 1)
+ else:
+ # TODO(EA2D): special-casing not needed with 2D EAs
+ values = concat_compat(vals)
+
+ b = make_block(values, placement=placement, ndim=blk.ndim)
  else:
  b = make_block(
  _concatenate_join_units(join_units, concat_axis, copy=copy),
@@ -419,13 +430,15 @@ def _get_empty_dtype_and_na(join_units):
  raise AssertionError(msg)
 
 
-def _is_uniform_join_units(join_units) -> bool:
+def _is_uniform_join_units(join_units: List[JoinUnit]) -> bool:
  """
  Check if the join units consist of blocks of uniform type that can
  be concatenated using Block.concat_same_type instead of the generic
  _concatenate_join_units (which uses `concat_compat`).
 
  """
+ # TODO: require dtype match in addition to same type? e.g. DatetimeTZBlock
+ # cannot necessarily join
  return (
  # all blocks need to have the same type
  all(type(ju.block) is type(join_units[0].block) for ju in join_units)

pandas/tests/extension/test_external_block.py

@@ -32,12 +32,6 @@ def df():
  return pd.DataFrame(block_manager)
 
 
-def test_concat_dataframe(df):
- # GH17728
- res = pd.concat([df, df])
- assert isinstance(res._mgr.blocks[1], CustomBlock)
-
-
 def test_concat_axis1(df):
  # GH17954
  df2 = pd.DataFrame({"c": [0.1, 0.2, 0.3]})