Indexing MultiIndex with NDFrame indexer fails if index of indexer does not contain 0

[toobaz]

Code Sample, a copy-pastable example if possible

In [2]: d = pd.DataFrame([[1, 1, 3],
   ...:                   [1, 2, 4],
   ...:                   [2, 2, 5]], columns=['a', 'b', 'c'])

In [3]: d.set_index(['a', 'b']).loc[pd.Series([1, 2])]
Out[3]: 
     c
a b   
1 1  3
  2  4
2 2  5

In [4]: d.set_index(['a', 'b']).loc[pd.Series([1, 2], index=[2,0])]
Out[4]: 
     c
a b   
1 1  3
  2  4
2 2  5

In [5]: d.set_index(['a', 'b']).loc[pd.Series([1, 2], index=[2,3])]
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-5-a23ad44827f6> in <module>()
----> 1 d.set_index(['a', 'b']).loc[pd.Series([1, 2], index=[2,3])]

/home/pietro/nobackup/repo/pandas/pandas/core/indexing.py in __getitem__(self, key)
   1339         else:
   1340             key = com._apply_if_callable(key, self.obj)
-> 1341             return self._getitem_axis(key, axis=0)
   1342 
   1343     def _is_scalar_access(self, key):

/home/pietro/nobackup/repo/pandas/pandas/core/indexing.py in _getitem_axis(self, key, axis)
   1527             if isinstance(labels, MultiIndex):
   1528                 if (not isinstance(key, tuple) and len(key) > 1 and
-> 1529                         not isinstance(key[0], tuple)):
   1530                     if isinstance(key, ABCSeries):
   1531                         # GH 14730

/home/pietro/nobackup/repo/pandas/pandas/core/series.py in __getitem__(self, key)
    604         key = com._apply_if_callable(key, self)
    605         try:
--> 606             result = self.index.get_value(self, key)
    607 
    608             if not is_scalar(result):

/home/pietro/nobackup/repo/pandas/pandas/indexes/base.py in get_value(self, series, key)
   2304         try:
   2305             return self._engine.get_value(s, k,
-> 2306                                           tz=getattr(series.dtype, 'tz', None))
   2307         except KeyError as e1:
   2308             if len(self) > 0 and self.inferred_type in ['integer', 'boolean']:

/home/pietro/nobackup/repo/pandas/pandas/index.pyx in pandas.index.IndexEngine.get_value (pandas/index.c:3992)()

/home/pietro/nobackup/repo/pandas/pandas/index.pyx in pandas.index.IndexEngine.get_value (pandas/index.c:3689)()

/home/pietro/nobackup/repo/pandas/pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4688)()

/home/pietro/nobackup/repo/pandas/pandas/src/hashtable_class_helper.pxi in pandas.hashtable.Int64HashTable.get_item (pandas/hashtable.c:13370)()

/home/pietro/nobackup/repo/pandas/pandas/src/hashtable_class_helper.pxi in pandas.hashtable.Int64HashTable.get_item (pandas/hashtable.c:13308)()

KeyError: 0

Problem description

The index of the indexer should not matter at all... and indeed there is no bug when indexing a (non-Multi)Index:

In [6]: d.set_index(['a']).loc[pd.Series([1, 2], index=[2,3])]
Out[6]: 
   b  c
a      
1  1  3
1  2  4
2  2  5

Expected Output

The same as d.set_index(['a', 'b']).loc[pd.Series([1, 2])].

A PR is on its way.

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.5.2.final.0 python-bits: 64 OS: Linux OS-release: 4.7.0-1-amd64 machine: x86_64 processor: byteorder: little LC_ALL: None LANG: it_IT.utf8 LOCALE: it_IT.UTF-8

pandas: 0.19.0+464.g0b28e5a
pytest: None
pip: 8.1.2
setuptools: 28.0.0
Cython: 0.23.4
numpy: 1.12.0
scipy: 0.18.1
xarray: None
IPython: 5.1.0.dev
sphinx: 1.4.8
patsy: 0.3.0-dev
dateutil: 2.5.3
pytz: 2015.7
blosc: None
bottleneck: 1.2.0
tables: 3.2.2
numexpr: 2.6.0
feather: None
matplotlib: 2.0.0rc2
openpyxl: None
xlrd: 1.0.0
xlwt: 1.1.2
xlsxwriter: 0.9.3
lxml: None
bs4: 4.5.1
html5lib: 0.999
httplib2: 0.9.1
apiclient: 1.5.2
sqlalchemy: 1.0.15
pymysql: None
psycopg2: None
jinja2: 2.8
s3fs: None
pandas_datareader: 0.2.1

[jreback]

ok this looks like a bug. IIRC we had a similar issue (maybe was yours)?

[toobaz]

There was #14730 (this bug might actually be a side effect of its fix, but I didn't check).

[jreback]

@toobaz ok, can you add those examples as confirmation tests (they look similar). if they pass, then add that issue as well in the whatsnew note.

[toobaz]

I'm lost... have you seen the PR? (#15425)

[jreback]

of course that is where they should be added

[toobaz]

OK, I asked because that issue is already in the whatsnew note

So: you suggest I add to the tests I already wrote the ones in this bug report, right? (except for the data content, they are exactly the same...)

[jreback]

ahh ok then