From 072ed398a19069dcfd169a0151ccad40bce8a654 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Tue, 16 Feb 2021 12:58:33 +0100
Subject: [PATCH 1/8] [ArrayManager] ENH: implement concat with axis=1
 (merge/join)

---
 .github/workflows/ci.yml                   |  1 +
 pandas/core/internals/array_manager.py     |  7 ++-
 pandas/core/internals/concat.py            | 55 +++++++++++++++++-----
 pandas/tests/frame/methods/test_drop.py    |  2 +-
 pandas/tests/frame/methods/test_explode.py |  5 --
 pandas/tests/frame/methods/test_join.py    | 10 ++--
 pandas/tests/io/formats/test_printing.py   |  2 +-
 pandas/tests/io/test_fsspec.py             |  2 +-
 pandas/tests/reshape/merge/test_join.py    |  3 ++
 pandas/tests/reshape/merge/test_merge.py   | 29 +++++++++---
 10 files changed, 79 insertions(+), 37 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index aec19e27a33e2..7bf6320b6653c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -153,6 +153,7 @@ jobs:
       run: |
         source activate pandas-dev
         pytest pandas/tests/frame/methods --array-manager
+        pytest pandas/tests/reshape/merge --array-manager
 
         # indexing iset related (temporary since other tests don't pass yet)
         pytest pandas/tests/frame/indexing/test_indexing.py::TestDataFrameIndexing::test_setitem_multi_index --array-manager
diff --git a/pandas/core/internals/array_manager.py b/pandas/core/internals/array_manager.py
index 083f32488acd4..a8254f870cbd5 100644
--- a/pandas/core/internals/array_manager.py
+++ b/pandas/core/internals/array_manager.py
@@ -754,10 +754,12 @@ def reindex_indexer(
         # ignored keywords
         consolidate: bool = True,
         only_slice: bool = False,
+        # ArrayManager specific keywords
+        do_integrity_check: bool = True,
     ) -> T:
         axis = self._normalize_axis(axis)
         return self._reindex_indexer(
-            new_axis, indexer, axis, fill_value, allow_dups, copy
+            new_axis, indexer, axis, fill_value, allow_dups, copy, do_integrity_check
         )
 
     def _reindex_indexer(
@@ -768,6 +770,7 @@ def _reindex_indexer(
         fill_value=None,
         allow_dups: bool = False,
         copy: bool = True,
+        do_integrity_check: bool = True,
     ) -> T:
         """
         Parameters
@@ -822,7 +825,7 @@ def _reindex_indexer(
         new_axes = list(self._axes)
         new_axes[axis] = new_axis
 
-        return type(self)(new_arrays, new_axes)
+        return type(self)(new_arrays, new_axes, do_integrity_check=do_integrity_check)
 
     def take(self, indexer, axis: int = 1, verify: bool = True, convert: bool = True):
         """
diff --git a/pandas/core/internals/concat.py b/pandas/core/internals/concat.py
index 01d8cde3e9af2..aa3987999b3b8 100644
--- a/pandas/core/internals/concat.py
+++ b/pandas/core/internals/concat.py
@@ -31,6 +31,47 @@
     from pandas import Index
 
 
+def concatenate_array_managers(
+    mgrs_indexers, axes: List[Index], concat_axis: int, copy: bool
+) -> Manager:
+    """
+    Concatenate array managers into one.
+
+    Parameters
+    ----------
+    mgrs_indexers : list of (ArrayManager, {axis: indexer,...}) tuples
+    axes : list of Index
+    concat_axis : int
+    copy : bool
+
+    Returns
+    -------
+    ArrayManager
+    """
+    # reindex all arrays
+    mgrs = []
+    for mgr, indexers in mgrs_indexers:
+        for ax, indexer in indexers.items():
+            mgr = mgr.reindex_indexer(
+                axes[ax], indexer, axis=ax, allow_dups=True, do_integrity_check=False
+            )
+        mgrs.append(mgr)
+
+    # concatting along the rows -> concat the reindexed arrays
+    # TODO(ArrayManager) doesn't yet preserve the correct dtype
+    if concat_axis == 1:
+        arrays = [
+            concat_compat([mgrs[i].arrays[j] for i in range(len(mgrs))])
+            for j in range(len(mgrs[0].arrays))
+        ]
+        return ArrayManager(arrays, [axes[1], axes[0]], do_integrity_check=False)
+    # concatting along the columns -> combine reindexed arrays in a single manager
+    else:
+        assert concat_axis == 0
+        arrays = list(itertools.chain.from_iterable([mgr.arrays for mgr in mgrs]))
+        return ArrayManager(arrays, [axes[1], axes[0]], do_integrity_check=False)
+
+
 def concatenate_block_managers(
     mgrs_indexers, axes: List[Index], concat_axis: int, copy: bool
 ) -> Manager:
@@ -49,19 +90,7 @@ def concatenate_block_managers(
     BlockManager
     """
     if isinstance(mgrs_indexers[0][0], ArrayManager):
-
-        if concat_axis == 1:
-            # TODO for now only fastpath without indexers
-            mgrs = [t[0] for t in mgrs_indexers]
-            arrays = [
-                concat_compat([mgrs[i].arrays[j] for i in range(len(mgrs))], axis=0)
-                for j in range(len(mgrs[0].arrays))
-            ]
-            return ArrayManager(arrays, [axes[1], axes[0]])
-        elif concat_axis == 0:
-            mgrs = [t[0] for t in mgrs_indexers]
-            arrays = list(itertools.chain.from_iterable([mgr.arrays for mgr in mgrs]))
-            return ArrayManager(arrays, [axes[1], axes[0]])
+        return concatenate_array_managers(mgrs_indexers, axes, concat_axis, copy)
 
     concat_plans = [
         _get_mgr_concatenation_plan(mgr, indexers) for mgr, indexers in mgrs_indexers
diff --git a/pandas/tests/frame/methods/test_drop.py b/pandas/tests/frame/methods/test_drop.py
index 4568cda24d5cf..2af5c8dd29842 100644
--- a/pandas/tests/frame/methods/test_drop.py
+++ b/pandas/tests/frame/methods/test_drop.py
@@ -155,7 +155,7 @@ def test_drop(self):
         assert return_value is None
         tm.assert_frame_equal(df, expected)
 
-    @td.skip_array_manager_not_yet_implemented
+    @td.skip_array_manager_not_yet_implemented  # TODO(ArrayManager) groupby
     def test_drop_multiindex_not_lexsorted(self):
         # GH#11640
 
diff --git a/pandas/tests/frame/methods/test_explode.py b/pandas/tests/frame/methods/test_explode.py
index be80dd49ff1fb..bd0901387eeed 100644
--- a/pandas/tests/frame/methods/test_explode.py
+++ b/pandas/tests/frame/methods/test_explode.py
@@ -1,14 +1,9 @@
 import numpy as np
 import pytest
 
-import pandas.util._test_decorators as td
-
 import pandas as pd
 import pandas._testing as tm
 
-# TODO(ArrayManager) concat with reindexing
-pytestmark = td.skip_array_manager_not_yet_implemented
-
 
 def test_error():
     df = pd.DataFrame(
diff --git a/pandas/tests/frame/methods/test_join.py b/pandas/tests/frame/methods/test_join.py
index 42694dc3ff37c..2bbc73da24033 100644
--- a/pandas/tests/frame/methods/test_join.py
+++ b/pandas/tests/frame/methods/test_join.py
@@ -3,15 +3,10 @@
 import numpy as np
 import pytest
 
-import pandas.util._test_decorators as td
-
 import pandas as pd
 from pandas import DataFrame, Index, MultiIndex, date_range, period_range
 import pandas._testing as tm
 
-# TODO(ArrayManager) concat with reindexing
-pytestmark = td.skip_array_manager_not_yet_implemented
-
 
 @pytest.fixture
 def frame_with_period_index():
@@ -234,8 +229,9 @@ def test_join(self, multiindex_dataframe_random_data):
         b = frame.loc[frame.index[2:], ["B", "C"]]
 
         joined = a.join(b, how="outer").reindex(frame.index)
-        expected = frame.copy()
-        expected.values[np.isnan(joined.values)] = np.nan
+        expected = frame.copy().values
+        expected[np.isnan(joined.values)] = np.nan
+        expected = DataFrame(expected, index=frame.index, columns=frame.columns)
 
         assert not np.isnan(joined.values).all()
 
diff --git a/pandas/tests/io/formats/test_printing.py b/pandas/tests/io/formats/test_printing.py
index 2339e21288bb5..24d1973eeda6d 100644
--- a/pandas/tests/io/formats/test_printing.py
+++ b/pandas/tests/io/formats/test_printing.py
@@ -121,7 +121,7 @@ def test_ambiguous_width(self):
         assert adjoined == expected
 
 
-@td.skip_array_manager_not_yet_implemented
+@td.skip_array_manager_not_yet_implemented  # TODO(ArrayManager) JSON
 class TestTableSchemaRepr:
     @classmethod
     def setup_class(cls):
diff --git a/pandas/tests/io/test_fsspec.py b/pandas/tests/io/test_fsspec.py
index d9575a6ad81e5..3131131682ccd 100644
--- a/pandas/tests/io/test_fsspec.py
+++ b/pandas/tests/io/test_fsspec.py
@@ -247,7 +247,7 @@ def test_pickle_options(fsspectest):
     tm.assert_frame_equal(df, out)
 
 
-@td.skip_array_manager_not_yet_implemented
+@td.skip_array_manager_not_yet_implemented  # TODO(ArrayManager) JSON
 def test_json_options(fsspectest):
     df = DataFrame({"a": [0]})
     df.to_json("testmem://afile", storage_options={"test": "json_write"})
diff --git a/pandas/tests/reshape/merge/test_join.py b/pandas/tests/reshape/merge/test_join.py
index 500d7000817af..242fc8cade9e6 100644
--- a/pandas/tests/reshape/merge/test_join.py
+++ b/pandas/tests/reshape/merge/test_join.py
@@ -1,6 +1,8 @@
 import numpy as np
 import pytest
 
+import pandas.util._test_decorators as td
+
 import pandas as pd
 from pandas import (
     Categorical,
@@ -547,6 +549,7 @@ def test_join_non_unique_period_index(self):
         )
         tm.assert_frame_equal(result, expected)
 
+    @td.skip_array_manager_not_yet_implemented  # TODO(ArrayManager) groupby
     def test_mixed_type_join_with_suffix(self):
         # GH #916
         df = DataFrame(np.random.randn(20, 6), columns=["a", "b", "c", "d", "e", "f"])
diff --git a/pandas/tests/reshape/merge/test_merge.py b/pandas/tests/reshape/merge/test_merge.py
index da3ac81c4aa17..e9591cc46dd26 100644
--- a/pandas/tests/reshape/merge/test_merge.py
+++ b/pandas/tests/reshape/merge/test_merge.py
@@ -277,17 +277,27 @@ def test_merge_copy(self):
         merged["d"] = "peekaboo"
         assert (right["d"] == "bar").all()
 
-    def test_merge_nocopy(self):
+    def test_merge_nocopy(self, using_array_manager):
         left = DataFrame({"a": 0, "b": 1}, index=range(10))
         right = DataFrame({"c": "foo", "d": "bar"}, index=range(10))
 
         merged = merge(left, right, left_index=True, right_index=True, copy=False)
 
-        merged["a"] = 6
-        assert (left["a"] == 6).all()
+        if using_array_manager:
+            # With ArrayManager, setting a column doesn't change the values inplace
+            # and thus does not propagate the changes to the original left/right
+            # dataframes -> need to check that no copy was made in a different way
+            # TODO(ArrayManager) we should be able to simplify this with a .loc
+            #  setitem test: merged.loc[0, "a"] = 10; assert left.loc[0, "a"] == 10
+            #  but this currently replaces the array (_setitem_with_indexer_split_path)
+            assert merged._mgr.arrays[0] is left._mgr.arrays[0]
+            assert merged._mgr.arrays[2] is right._mgr.arrays[0]
+        else:
+            merged["a"] = 6
+            assert (left["a"] == 6).all()
 
-        merged["d"] = "peekaboo"
-        assert (right["d"] == "peekaboo").all()
+            merged["d"] = "peekaboo"
+            assert (right["d"] == "peekaboo").all()
 
     def test_intelligently_handle_join_key(self):
         # #733, be a bit more 1337 about not returning unconsolidated DataFrame
@@ -1362,7 +1372,7 @@ def test_merge_take_missing_values_from_index_of_other_dtype(self):
         expected = expected.reindex(columns=["a", "key", "b"])
         tm.assert_frame_equal(result, expected)
 
-    def test_merge_readonly(self):
+    def test_merge_readonly(self, using_array_manager):
         # https://github.com/pandas-dev/pandas/issues/27943
         data1 = DataFrame(
             np.arange(20).reshape((4, 5)) + 1, columns=["a", "b", "c", "d", "e"]
@@ -1371,7 +1381,12 @@ def test_merge_readonly(self):
             np.arange(20).reshape((5, 4)) + 1, columns=["a", "b", "x", "y"]
         )
 
-        data1._mgr.blocks[0].values.flags.writeable = False
+        if using_array_manager:
+            for arr in data1._mgr.arrays:
+                arr.flags.writeable = False
+        else:
+            data1._mgr.blocks[0].values.flags.writeable = False
+
         data1.merge(data2)  # no error
 
 

From 31cfb0d5d0ebe303c820b6684f64c824e8c5a565 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Wed, 17 Feb 2021 11:00:35 +0100
Subject: [PATCH 2/8] address feedback

---
 pandas/core/internals/array_manager.py | 1 +
 pandas/core/internals/concat.py        | 7 ++++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/pandas/core/internals/array_manager.py b/pandas/core/internals/array_manager.py
index ddac75ce81071..28e9ce6885e21 100644
--- a/pandas/core/internals/array_manager.py
+++ b/pandas/core/internals/array_manager.py
@@ -756,6 +756,7 @@ def reindex_indexer(
         self: T,
         new_axis,
         indexer,
+        *,
         axis: int,
         fill_value=None,
         allow_dups: bool = False,
diff --git a/pandas/core/internals/concat.py b/pandas/core/internals/concat.py
index 141e9f42a350a..99bc9ac337728 100644
--- a/pandas/core/internals/concat.py
+++ b/pandas/core/internals/concat.py
@@ -75,16 +75,16 @@ def concatenate_array_managers(
             )
         mgrs.append(mgr)
 
-    # concatting along the rows -> concat the reindexed arrays
-    # TODO(ArrayManager) doesn't yet preserve the correct dtype
     if concat_axis == 1:
+        # concatting along the rows -> concat the reindexed arrays
+        # TODO(ArrayManager) doesn't yet preserve the correct dtype
         arrays = [
             concat_compat([mgrs[i].arrays[j] for i in range(len(mgrs))])
             for j in range(len(mgrs[0].arrays))
         ]
         return ArrayManager(arrays, [axes[1], axes[0]], do_integrity_check=False)
-    # concatting along the columns -> combine reindexed arrays in a single manager
     else:
+        # concatting along the columns -> combine reindexed arrays in a single manager
         assert concat_axis == 0
         arrays = list(itertools.chain.from_iterable([mgr.arrays for mgr in mgrs]))
         return ArrayManager(arrays, [axes[1], axes[0]], do_integrity_check=False)
@@ -107,6 +107,7 @@ def concatenate_block_managers(
     -------
     BlockManager
     """
+    # TODO(ArrayManager) this assumes that all managers are of the same type
     if isinstance(mgrs_indexers[0][0], ArrayManager):
         return concatenate_array_managers(mgrs_indexers, axes, concat_axis, copy)
 

From 3488d63d6bba41663a39ca097e7f2a22663c4c54 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Thu, 18 Feb 2021 14:31:06 +0100
Subject: [PATCH 3/8] add array property

---
 pandas/core/internals/managers.py        | 12 ++++++++++++
 pandas/tests/reshape/merge/test_merge.py |  7 ++-----
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/pandas/core/internals/managers.py b/pandas/core/internals/managers.py
index b3f0466f236b6..29dc5b14fdd35 100644
--- a/pandas/core/internals/managers.py
+++ b/pandas/core/internals/managers.py
@@ -282,6 +282,18 @@ def get_dtypes(self):
         dtypes = np.array([blk.dtype for blk in self.blocks])
         return algos.take_nd(dtypes, self.blknos, allow_fill=False)
 
+    @property
+    def arrays(self):
+        """
+        Quick access to the backing arrays of the Blocks.
+
+        Only for compatibility with ArrayManager for testing convenience.
+        Not to be used in actual code, and return value is not the same as the
+        ArrayManager method (list of 1D arrays vs iterator of 2D ndarrays / 1D EAs).
+        """
+        for blk in self.blocks:
+            yield blk.values
+
     def __getstate__(self):
         block_values = [b.values for b in self.blocks]
         block_items = [self.items[b.mgr_locs.indexer] for b in self.blocks]
diff --git a/pandas/tests/reshape/merge/test_merge.py b/pandas/tests/reshape/merge/test_merge.py
index 72afea7ba3e8d..483a9488be70d 100644
--- a/pandas/tests/reshape/merge/test_merge.py
+++ b/pandas/tests/reshape/merge/test_merge.py
@@ -1391,11 +1391,8 @@ def test_merge_readonly(self, using_array_manager):
             np.arange(20).reshape((5, 4)) + 1, columns=["a", "b", "x", "y"]
         )
 
-        if using_array_manager:
-            for arr in data1._mgr.arrays:
-                arr.flags.writeable = False
-        else:
-            data1._mgr.blocks[0].values.flags.writeable = False
+        for arr in data1._mgr.arrays:
+            arr.flags.writeable = False
 
         data1.merge(data2)  # no error
 

From 437c1d24bae42e9903fa46ea60140b434fd2f852 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Thu, 18 Feb 2021 14:40:47 +0100
Subject: [PATCH 4/8] simplify do_integrity_check

---
 pandas/core/internals/array_manager.py | 7 ++-----
 pandas/core/internals/concat.py        | 4 +---
 2 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/pandas/core/internals/array_manager.py b/pandas/core/internals/array_manager.py
index 28e9ce6885e21..1655d7bd28f08 100644
--- a/pandas/core/internals/array_manager.py
+++ b/pandas/core/internals/array_manager.py
@@ -764,12 +764,10 @@ def reindex_indexer(
         # ignored keywords
         consolidate: bool = True,
         only_slice: bool = False,
-        # ArrayManager specific keywords
-        do_integrity_check: bool = True,
     ) -> T:
         axis = self._normalize_axis(axis)
         return self._reindex_indexer(
-            new_axis, indexer, axis, fill_value, allow_dups, copy, do_integrity_check
+            new_axis, indexer, axis, fill_value, allow_dups, copy
         )
 
     def _reindex_indexer(
@@ -780,7 +778,6 @@ def _reindex_indexer(
         fill_value=None,
         allow_dups: bool = False,
         copy: bool = True,
-        do_integrity_check: bool = True,
     ) -> T:
         """
         Parameters
@@ -835,7 +832,7 @@ def _reindex_indexer(
         new_axes = list(self._axes)
         new_axes[axis] = new_axis
 
-        return type(self)(new_arrays, new_axes, do_integrity_check=do_integrity_check)
+        return type(self)(new_arrays, new_axes, do_integrity_check=False)
 
     def take(self, indexer, axis: int = 1, verify: bool = True, convert: bool = True):
         """
diff --git a/pandas/core/internals/concat.py b/pandas/core/internals/concat.py
index 99bc9ac337728..a294677cf4e05 100644
--- a/pandas/core/internals/concat.py
+++ b/pandas/core/internals/concat.py
@@ -70,9 +70,7 @@ def concatenate_array_managers(
     mgrs = []
     for mgr, indexers in mgrs_indexers:
         for ax, indexer in indexers.items():
-            mgr = mgr.reindex_indexer(
-                axes[ax], indexer, axis=ax, allow_dups=True, do_integrity_check=False
-            )
+            mgr = mgr.reindex_indexer(axes[ax], indexer, axis=ax, allow_dups=True)
         mgrs.append(mgr)
 
     if concat_axis == 1:

From 2597cd5461c5c0dd43c116f30e8fe87b1cbc2b26 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Thu, 18 Feb 2021 14:42:12 +0100
Subject: [PATCH 5/8] clean-up unused using_array_manager

---
 pandas/tests/reshape/merge/test_merge.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/tests/reshape/merge/test_merge.py b/pandas/tests/reshape/merge/test_merge.py
index 483a9488be70d..eef8e75b8e111 100644
--- a/pandas/tests/reshape/merge/test_merge.py
+++ b/pandas/tests/reshape/merge/test_merge.py
@@ -1382,7 +1382,7 @@ def test_merge_take_missing_values_from_index_of_other_dtype(self):
         expected = expected.reindex(columns=["a", "key", "b"])
         tm.assert_frame_equal(result, expected)
 
-    def test_merge_readonly(self, using_array_manager):
+    def test_merge_readonly(self):
         # https://github.com/pandas-dev/pandas/issues/27943
         data1 = DataFrame(
             np.arange(20).reshape((4, 5)) + 1, columns=["a", "b", "c", "d", "e"]

From 31d1305fc24cc32c97cb3ca028615a2822f202b8 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Thu, 18 Feb 2021 15:39:04 +0100
Subject: [PATCH 6/8] remove keyword-only indicator

---
 pandas/core/internals/array_manager.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/pandas/core/internals/array_manager.py b/pandas/core/internals/array_manager.py
index 1655d7bd28f08..e1bde790e16e4 100644
--- a/pandas/core/internals/array_manager.py
+++ b/pandas/core/internals/array_manager.py
@@ -756,7 +756,6 @@ def reindex_indexer(
         self: T,
         new_axis,
         indexer,
-        *,
         axis: int,
         fill_value=None,
         allow_dups: bool = False,

From 3f5fc380f4ca8d856a7bb089fe16f4941856403e Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Tue, 23 Feb 2021 09:53:18 +0100
Subject: [PATCH 7/8] concatenate_block_managers -> concatenate_managers

---
 pandas/core/internals/__init__.py | 4 ++--
 pandas/core/internals/concat.py   | 2 +-
 pandas/core/reshape/concat.py     | 4 ++--
 pandas/core/reshape/merge.py      | 6 +++---
 4 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/pandas/core/internals/__init__.py b/pandas/core/internals/__init__.py
index 132598e03d6c0..054ce8a40288b 100644
--- a/pandas/core/internals/__init__.py
+++ b/pandas/core/internals/__init__.py
@@ -12,7 +12,7 @@
     TimeDeltaBlock,
     make_block,
 )
-from pandas.core.internals.concat import concatenate_block_managers
+from pandas.core.internals.concat import concatenate_managers
 from pandas.core.internals.managers import (
     BlockManager,
     SingleBlockManager,
@@ -35,7 +35,7 @@
     "ArrayManager",
     "BlockManager",
     "SingleBlockManager",
-    "concatenate_block_managers",
+    "concatenate_managers",
     # those two are preserved here for downstream compatibility (GH-33892)
     "create_block_manager_from_arrays",
     "create_block_manager_from_blocks",
diff --git a/pandas/core/internals/concat.py b/pandas/core/internals/concat.py
index 44284023745cd..362f2fde47e0b 100644
--- a/pandas/core/internals/concat.py
+++ b/pandas/core/internals/concat.py
@@ -88,7 +88,7 @@ def concatenate_array_managers(
         return ArrayManager(arrays, [axes[1], axes[0]], do_integrity_check=False)
 
 
-def concatenate_block_managers(
+def concatenate_managers(
     mgrs_indexers, axes: List[Index], concat_axis: int, copy: bool
 ) -> Manager:
     """
diff --git a/pandas/core/reshape/concat.py b/pandas/core/reshape/concat.py
index 92fc4a2e85163..a8c6913cd5d6c 100644
--- a/pandas/core/reshape/concat.py
+++ b/pandas/core/reshape/concat.py
@@ -43,7 +43,7 @@
     get_unanimous_names,
 )
 import pandas.core.indexes.base as ibase
-from pandas.core.internals import concatenate_block_managers
+from pandas.core.internals import concatenate_managers
 
 if TYPE_CHECKING:
     from pandas import (
@@ -524,7 +524,7 @@ def get_result(self):
 
                 mgrs_indexers.append((obj._mgr, indexers))
 
-            new_data = concatenate_block_managers(
+            new_data = concatenate_managers(
                 mgrs_indexers, self.new_axes, concat_axis=self.bm_axis, copy=self.copy
             )
             if not self.copy:
diff --git a/pandas/core/reshape/merge.py b/pandas/core/reshape/merge.py
index 79d018427aa33..217d9915f834c 100644
--- a/pandas/core/reshape/merge.py
+++ b/pandas/core/reshape/merge.py
@@ -76,7 +76,7 @@
 import pandas.core.common as com
 from pandas.core.construction import extract_array
 from pandas.core.frame import _merge_doc
-from pandas.core.internals import concatenate_block_managers
+from pandas.core.internals import concatenate_managers
 from pandas.core.sorting import is_int64_overflow_possible
 
 if TYPE_CHECKING:
@@ -720,7 +720,7 @@ def get_result(self):
         lindexers = {1: left_indexer} if left_indexer is not None else {}
         rindexers = {1: right_indexer} if right_indexer is not None else {}
 
-        result_data = concatenate_block_managers(
+        result_data = concatenate_managers(
             [(self.left._mgr, lindexers), (self.right._mgr, rindexers)],
             axes=[llabels.append(rlabels), join_index],
             concat_axis=0,
@@ -1616,7 +1616,7 @@ def get_result(self):
         lindexers = {1: left_join_indexer} if left_join_indexer is not None else {}
         rindexers = {1: right_join_indexer} if right_join_indexer is not None else {}
 
-        result_data = concatenate_block_managers(
+        result_data = concatenate_managers(
             [(self.left._mgr, lindexers), (self.right._mgr, rindexers)],
             axes=[llabels.append(rlabels), join_index],
             concat_axis=0,

From 54692cadd39d22f98c230c01da85181c9ffb7937 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Tue, 23 Feb 2021 09:55:02 +0100
Subject: [PATCH 8/8] add comment

---
 pandas/tests/reshape/merge/test_merge.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pandas/tests/reshape/merge/test_merge.py b/pandas/tests/reshape/merge/test_merge.py
index eef8e75b8e111..e1b1e80a29a43 100644
--- a/pandas/tests/reshape/merge/test_merge.py
+++ b/pandas/tests/reshape/merge/test_merge.py
@@ -1391,6 +1391,7 @@ def test_merge_readonly(self):
             np.arange(20).reshape((5, 4)) + 1, columns=["a", "b", "x", "y"]
         )
 
+        # make each underlying block array / column array read-only
         for arr in data1._mgr.arrays:
             arr.flags.writeable = False