str.extractall gives ValueError: Length of names must match number of levels in MultiIndex.

[lmudge]

Code Sample, a copy-pastable example if possible

s = Series(["HCPSS_000_123", "HCPSS_100_1234", "HCPSS_200_1234"], index=["CM_1","CM_2","CM_3"])
module = s.str.extractall("HCPSS_(\d{3})")

Gives the following error

ValueError Traceback (most recent call last)
in ()
----> 1 module = s.str.extractall("HCPSS_(\d{3})")

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\core\strings.pyc in extractall(self, pat, flags)
1619 @copy(str_extractall)
1620 def extractall(self, pat, flags=0):
-> 1621 return str_extractall(self._orig, pat, flags=flags)
1622
1623 _shared_docs['find'] = ("""

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\core\strings.pyc in str_extractall(arr, pat, flags)
711 if 0 < len(index_list):
712 index = MultiIndex.from_tuples(
--> 713 index_list, names=arr.index.names + ["match"])
714 else:
715 index = None

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\indexes\multi.pyc in from_tuples(cls, tuples, sortorder, names)
893 arrays = lzip(*tuples)
894
--> 895 return MultiIndex.from_arrays(arrays, sortorder=sortorder, names=names)
896
897 @classmethod

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\indexes\multi.pyc in from_arrays(cls, arrays, sortorder, names)
848
849 return MultiIndex(levels=levels, labels=labels, sortorder=sortorder,
--> 850 names=names, verify_integrity=False)
851
852 @classmethod

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\indexes\multi.pyc in new(cls, levels, labels, sortorder, names, copy, verify_integrity, _set_identity, name, **kwargs)
95 if names is not None:
96 # handles name validation
---> 97 result._set_names(names)
98
99 if sortorder is not None:

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\indexes\multi.pyc in _set_names(self, names, level, validate)
450 raise ValueError('Length of names must match length of level.')
451 if validate and level is None and len(names) != self.nlevels:
--> 452 raise ValueError('Length of names must match number of levels in '
453 'MultiIndex.')
454

ValueError: Length of names must match number of levels in MultiIndex.

Expected Output

No error

output of pd.show_versions()

INSTALLED VERSIONS

commit: None
python: 2.7.12.final.0
python-bits: 64
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 78 Stepping 3, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.18.1
nose: 1.3.7
pip: 8.1.2
setuptools: 23.0.0
Cython: 0.24
numpy: 1.11.1
scipy: 0.17.1
statsmodels: 0.6.1
xarray: None
IPython: 4.2.0
sphinx: 1.4.1
patsy: 0.4.1
dateutil: 2.5.3
pytz: 2016.4
blosc: None
bottleneck: 1.1.0
tables: 3.2.2
numexpr: 2.6.0
matplotlib: 1.5.1
openpyxl: 2.3.2
xlrd: 1.0.0
xlwt: 1.1.2
xlsxwriter: 0.9.2
lxml: 3.6.0
bs4: 4.4.1
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.13
pymysql: None
psycopg2: None
jinja2: 2.8
boto: 2.40.0
pandas_datareader: None

[jreback]

Looks like solved in #13156

In [9]: module
Out[9]: 
              0
     match     
CM_1 0      000
CM_2 0      100
CM_3 0      200

In [10]: s
Out[10]: 
CM_1     HCPSS_000_123
CM_2    HCPSS_100_1234
CM_3    HCPSS_200_1234
dtype: object

In [11]: pd.__version__
Out[11]: '0.19.0rc1+23.gdb9dc65'

[jorisvandenbossche]

@lmudge BTW, I think in this case you rather want to use extract instead of extractall