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BUG: Fixed nlargest/smallest functionality for dataframes with MultiIndex columns #23034

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Merged
merged 7 commits into from
Oct 24, 2018
Merged

BUG: Fixed nlargest/smallest functionality for dataframes with MultiIndex columns #23034

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1bf67cf
By convention, tuples indicate multi-level lookups. This change fixes…
Oct 8, 2018
1910ca4
Fixed tests (tuples are reserved for multi-level lookups)
Oct 8, 2018
06bfd0a
Added test coverage for multi-level (tuple) lookups.
Oct 8, 2018
5530b9a
Updated test: Added github issue id and used 'tm' instead of 'pd.util…
Oct 11, 2018
d8abc0c
Added whatsnew note in Bug Fixes / Reshaping
Oct 11, 2018
b65c6a0
Fixed typo
Oct 11, 2018
f77f164
fixed whatsnew note: was in wrong section
Oct 23, 2018
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v0.24.0.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -1194,6 +1194,7 @@ Reshaping
- Bug in :func:`merge_asof` when merging on float values within defined tolerance (:issue:`22981`)
- Bug in :func:`pandas.concat` when concatenating a multicolumn DataFrame with tz-aware data against a DataFrame with a different number of columns (:issue`22796`)
- Bug in :func:`merge_asof` where confusing error message raised when attempting to merge with missing values (:issue:`23189`)
- Bug in :meth:`DataFrame.nsmallest` and :meth:`DataFrame.nlargest` for dataframes that have :class:`MultiIndex`ed columns (:issue:`23033`).

.. _whatsnew_0240.bug_fixes.sparse:

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2 changes: 1 addition & 1 deletion pandas/core/algorithms.py
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Expand Up @@ -1161,7 +1161,7 @@ class SelectNFrame(SelectN):

def __init__(self, obj, n, keep, columns):
super(SelectNFrame, self).__init__(obj, n, keep)
if not is_list_like(columns):
if not is_list_like(columns) or isinstance(columns, tuple):
columns = [columns]
columns = list(columns)
self.columns = columns
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19 changes: 18 additions & 1 deletion pandas/tests/frame/test_analytics.py
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Expand Up @@ -2153,7 +2153,7 @@ def test_n(self, df_strings, nselect_method, n, order):
tm.assert_frame_equal(result, expected)

@pytest.mark.parametrize('columns', [
('group', 'category_string'), ('group', 'string')])
['group', 'category_string'], ['group', 'string']])
def test_n_error(self, df_main_dtypes, nselect_method, columns):
df = df_main_dtypes
col = columns[1]
Expand Down Expand Up @@ -2259,3 +2259,20 @@ def test_series_nat_conversion(self):
df.rank()
result = df
tm.assert_frame_equal(result, expected)

def test_multiindex_column_lookup(self):
# Check whether tuples are correctly treated as multi-level lookups.
# GH 23033
df = pd.DataFrame(
columns=pd.MultiIndex.from_product([['x'], ['a', 'b']]),
data=[[0.33, 0.13], [0.86, 0.25], [0.25, 0.70], [0.85, 0.91]])

# nsmallest
result = df.nsmallest(3, ('x', 'a'))
expected = df.iloc[[2, 0, 3]]
tm.assert_frame_equal(result, expected)

# nlargest
result = df.nlargest(3, ('x', 'b'))
expected = df.iloc[[3, 2, 1]]
tm.assert_frame_equal(result, expected)