Using tuples as dataframe index, containing single entry makes rows impossible to select

[zilion22]

Code Sample

print "-- Good example --"
df=pd.DataFrame([[tuple([1,2])],[tuple([1])]], columns=['a']).set_index('a')
z=df.index[0]
df.loc[[z]]

print "-- Buggy example --"
z=df.index[1]
df.loc[[z]]

Results in:

-- Good example --
a
(1, 2)

-- Buggy example --

KeyErrorTraceback (most recent call last)
in ()
10 print "-- Bug example --"
11 z=df.index[1]
---> 12 df.loc[[z]]

/usr/lib64/python2.7/site-packages/pandas/core/indexing.pyc in getitem(self, key)
1371
1372 maybe_callable = com._apply_if_callable(key, self.obj)
-> 1373 return self._getitem_axis(maybe_callable, axis=axis)
1374
1375 def _is_scalar_access(self, key):

/usr/lib64/python2.7/site-packages/pandas/core/indexing.pyc in _getitem_axis(self, key, axis)
1614 raise ValueError('Cannot index with multidimensional key')
1615
-> 1616 return self._getitem_iterable(key, axis=axis)
1617
1618 # nested tuple slicing

/usr/lib64/python2.7/site-packages/pandas/core/indexing.pyc in _getitem_iterable(self, key, axis)
1113
1114 if self._should_validate_iterable(axis):
-> 1115 self._has_valid_type(key, axis)
1116
1117 labels = self.obj._get_axis(axis)

/usr/lib64/python2.7/site-packages/pandas/core/indexing.pyc in _has_valid_type(self, key, axis)
1470 raise KeyError(
1471 u"None of [{key}] are in the [{axis}]".format(
-> 1472 key=key, axis=self.obj._get_axis_name(axis)))
1473 else:
1474

KeyError: u'None of [[(1,)]] are in the [index]'

Problem description

I wanted to use tuples as an indexer.
However if the tuple contains only one entry, it makes lines to be impossible to select since it brakes pandas.

Expected Output

-- Good example --
a
(1, 2)

-- Buggy example --
a
(1, )

Output of pd.show_versions()

[paste the output of pd.show_versions() here below this line]

INSTALLED VERSIONS

commit: None
python: 2.7.5.final.0
python-bits: 64
OS: Linux
OS-release: 3.10.0-693.5.2.el7.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: None.None

pandas: 0.22.0
pytest: 3.1.2
pip: 10.0.1
setuptools: None
Cython: 0.24
numpy: 1.14.0
scipy: 1.0.0
pyarrow: None
xarray: None
IPython: 5.6.0
sphinx: 1.6.2
patsy: 0.4.1
dateutil: 2.7.2
pytz: 2017.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.0.0
openpyxl: 2.5.0
xlrd: 1.1.0
xlwt: 1.3.0
xlsxwriter: 1.0.2
lxml: 4.1.1
bs4: None
html5lib: 1.0.1
sqlalchemy: 1.0.13
pymysql: None
psycopg2: 2.6.1 (dt dec pq3 ext)
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

[chris-b1]

If it can be avoided you probably don't want to be using tuples as indexes - it won't be as performant and isn't idiomatic - inference causes odd stuff like this to happen.

That said you are welcome to have a look and if you can fix this case without impacting existing tests, would certainly take a PR.

[toobaz]

This works correctly now, but probably isn't tested