Resampling fails with equal frequency

[richjoyce]

I've got a DataFrame with a TimedeltaIndex that fails when I try to resample it to the same frequency.

Minimal working example

import pandas as pd
index = pd.timedelta_range('0', periods=9, freq='10L')
series = pd.Series(range(9), index=index)
series.resample('10L') # throws ValueError

pandas versions

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.10.final.0
python-bits: 64
OS: Darwin
OS-release: 14.5.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.17.1
nose: None
pip: 1.4.1
setuptools: 1.1.6
Cython: None
numpy: 1.8.0rc1
scipy: 0.13.0b1
statsmodels: None
IPython: 2.0.0
sphinx: 1.2.2
patsy: None
dateutil: 1.5
pytz: 2013.7
blosc: None
bottleneck: None
tables: None
numexpr: 2.4.6
matplotlib: 1.3.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
Jinja2: None

The error thrown is:

pandas/tseries/resample.pyc in _resample_timestamps(self, kind)
    306                     axlabels.inferred_freq) == self.freq:
    307                     result = obj.copy()
--> 308                     result.index = res_index
    309                 else:
    310                     result = obj.reindex(res_index, method=self.fill_method,
... (more stacks skipped) ...
ValueError: Length mismatch: Expected axis has 9 elements, new values have 8 elements

This appears to be a problem with the logic in TimeGrouper._resample_timestamps() lines 298 to 308, the error is being thrown on line 308. It looks like res_index is being set to the wrong thing but I'm not familiar enough with the code to know how to fix properly.

[jreback]

this is fixed in the resample refactor, #11841
but will add as a confirming test.