ERR: invalid MultiIndex construction · Issue #17464 · pandas-dev/pandas (original) (raw)

Code Sample, a copy-pastable example if possible

import pandas as pd import numpy as np idx0 = range(2) idx1 = np.repeat(range(2), 2)

midx = pd.MultiIndex( levels=[idx0, idx1], labels=[ np.repeat(range(len(idx0)), len(idx1)), np.tile(range(len(idx1)), len(idx0)) ], names=['idx0', 'idx1'] )

df = pd.DataFrame( [ [i2/float(j), 'example{}'.format(i), i3/float(j)] for j in range(1, len(idx0) + 1) for i in range(1, len(idx1) + 1) ], columns=['col0', 'col1', 'col2'], index=midx )

example = df.loc[[(0, 1)]]

For display

In [13]: example Out[13]: col0 col1 col2 idx0 idx1 0 1 16.0 example4 64.0

Problem description

Taken from this StackOverflow post:

https://stackoverflow.com/q/46098097/4013571

Given the following dataframe

       col0      col1  col2

idx0 idx1 0 0 1.0 example1 1.0 0 4.0 example2 8.0 1 9.0 example3 27.0 1 16.0 example4 64.0 1 0 0.5 example1 0.5 0 2.0 example2 4.0 1 4.5 example3 13.5 1 8.0 example4 32.0

the .xs operation will select

In [121]: df.xs((0,1), level=[0,1]) Out[121]: col0 col1 col2 idx0 idx1 0 1 9.0 example3 27.0 1 16.0 example4 64.0

whilst the .loc operation will select

In [125]: df.loc[[(0,1)]] Out[125]: col0 col1 col2 idx0 idx1 0 1 16.0 example4 64.0

This is highlighted even further by the following

In [149]: df.loc[pd.IndexSlice[:, 1], :] Out[149]: col0 col1 col2 idx0 idx1 0 1 9.0 example3 27.0 1 16.0 example4 64.0

In [150]: df.loc[pd.IndexSlice[0, 1], :] Out[150]: col0 16 col1 example4 col2 64 Name: (0, 1), dtype: object

Expected Output

Note that this only works for this minimal example because there is only one label in level 0 index axis

In [8]: df.loc[pd.IndexSlice[:, 1], :] Out[8]: col0 col1 col2 idx0 idx1 0 1 9.0 example3 27.0 1 16.0 example4 64.0

Output of `pd.show_versions()`

INSTALLED VERSIONS

commit: None
python: 2.7.13.final.0
python-bits: 64
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 79 Stepping 1, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None