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Maintain Dict Ordering with Concat #21512

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Maintain Dict Ordering with Concat #21512

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87bb1ac
Fixes #21510 Remove sort if its already an ordered dict
SaturninoMateus Jun 16, 2018
f9d105e
Adding a space and new line to match PEP8. #21510
SaturninoMateus Jun 16, 2018
b044e04
Adding test case for concat OrderedDict and updating . #21510
SaturninoMateus Jun 17, 2018
eaa7cc0
Fixing v0.23.2.txt syntax . #21510
SaturninoMateus Jun 17, 2018
6869e2c
Improving test case for orderedDict and whatsnew info. #21510
SaturninoMateus Jun 17, 2018
e9561fe
Refactoring test case code for orderedDict and improving whatsnew inf…
SaturninoMateus Jun 19, 2018
53aca81
Fixing spaces to match with PEP8. #21510
SaturninoMateus Jun 19, 2018
726755f
Merging upstream/master into my dev branch
SaturninoMateus Jun 21, 2018
a7aa052
Adding info about pd.concat method into whatsnew 0.24.0 #21510
SaturninoMateus Jun 21, 2018
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1 change: 1 addition & 0 deletions .gitignore
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Expand Up @@ -110,3 +110,4 @@ doc/source/styled.xlsx
doc/source/templates/
env/
doc/source/savefig/
*my-dev-test.py
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what is this from?

2 changes: 1 addition & 1 deletion doc/source/whatsnew/v0.24.0.txt
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Expand Up @@ -255,6 +255,6 @@ Other
^^^^^

- :meth: `~pandas.io.formats.style.Styler.background_gradient` now takes a ``text_color_threshold`` parameter to automatically lighten the text color based on the luminance of the background color. This improves readability with dark background colors without the need to limit the background colormap range. (:issue:`21258`)
-
- Bug in :meth:`concat` should maintain dict order when :meth:`concat` is called (:issue:`2151`)
-
-
7 changes: 5 additions & 2 deletions pandas/core/reshape/concat.py
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@@ -1,7 +1,7 @@
"""
concat routines
"""

from collections import OrderedDict
import numpy as np
from pandas import compat, DataFrame, Series, Index, MultiIndex
from pandas.core.index import (_get_objs_combined_axis,
Expand Down Expand Up @@ -250,7 +250,10 @@ def __init__(self, objs, axis=0, join='outer', join_axes=None,

if isinstance(objs, dict):
if keys is None:
keys = sorted(objs)
if not isinstance(objs, OrderedDict):
keys = sorted(objs)
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Normal dicts are ordered too in python3.6+, that must be checked too. There is a PY36 constant somewhere, that you can use for this check.

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Not sure if we already took a stance on this as a project, but the orderedness of dicts in 3.6 is considered an implementation detail of cpython, while it will be a language feature starting from 3.7 . So in principle in 3.6 users should not rely on it, and we should not assume they do.

@topper-123 's comment still holds I think, but for 3.7

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Well we've already relied on that implementation detail in other changes (see #19830, #19859, #19884) so I'd be +1 on relying on that here as well

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Yeah, given that Python 3.6 is at 3.6.5 now, and its's being formalised in 3.7, I think this is quite safe. They're not going to change implementation now...

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This is very simliar to in structure to pandas.core.common._dict_keys_to_ordered_list. structure like this. see if we can consolidate all of these try/sorting routings.

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@jreback you mean use: keys = com._dict_keys_to_ordered_list(objs) ? If so, I'm afraid we'll need to refactor _dict_keys_to_ordered_list because it assumes that PY36 has sorted dict which I think its not always true, and will break test_concat_dict test case.

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yes that's the point i am raising, I want a refactor here.

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So, from _dict_keys_to_ordered_list method, i suggest change the conditionif PY36 or isinstance(mapping, OrderedDict): to if PY37 or isinstance(mapping, OrderedDict): then, remove test_constructor_dict_order_insertion and test_constructor_dict_order. What do you think about it?

else:
keys = objs
objs = [objs[k] for k in keys]
else:
objs = list(objs)
Expand Down
12 changes: 12 additions & 0 deletions pandas/tests/reshape/test_concat.py
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@@ -1,3 +1,4 @@
from collections import OrderedDict
from warnings import catch_warnings
from itertools import combinations, product

Expand Down Expand Up @@ -1294,6 +1295,17 @@ def test_concat_rename_index(self):
tm.assert_frame_equal(result, exp)
assert result.index.names == exp.index.names

def test_concat_with_ordered_dict(self):
# GH 21510
result = pd.concat(OrderedDict([('First', pd.Series(range(3))),
('Another', pd.Series(range(4)))]))
index = MultiIndex(levels=[['First', 'Another'], [0, 1, 2, 3]],
labels=[[0, 0, 0, 1, 1, 1, 1],
[0, 1, 2, 0, 1, 2, 3]])
data = list(range(3)) + list(range(4))
expected = pd.Series(data, index=index)
tm.assert_series_equal(result, expected)

def test_crossed_dtypes_weird_corner(self):
columns = ['A', 'B', 'C', 'D']
df1 = DataFrame({'A': np.array([1, 2, 3, 4], dtype='f8'),
Expand Down