Reindex on nearest datetime gives UFuncTypeError - subtract with dtype('<M8[ns]') and dtype('O')

[andrewcooke]

Code Sample

import pandas as pd
print(pd.__version__)
i1 = pd.DatetimeIndex(['2016-06-26 14:27:26+00:00'])
i2 = pd.DatetimeIndex(['2016-07-04 14:00:59+00:00'])
f2 = pd.DataFrame(index=i2)
f2.reindex(i1, method='nearest')

Problem description

Running the above code gives:

Python 3.7.4 (default, Jul 27 2019, 21:25:02) 
[GCC 7.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pandas as pd
>>> print(pd.__version__)
1.0.1
>>> i1 = pd.DatetimeIndex(['2016-06-26 14:27:26+00:00'])
>>> i2 = pd.DatetimeIndex(['2016-07-04 14:00:59+00:00'])
>>> f2 = pd.DataFrame(index=i2)
>>> f2.reindex(i1, method='nearest')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/andrew/project/ch2/choochoo/py/env/lib/python3.7/site-packages/pandas/util/_decorators.py", line 227, in wrapper
    return func(*args, **kwargs)
  File "/home/andrew/project/ch2/choochoo/py/env/lib/python3.7/site-packages/pandas/core/frame.py", line 3856, in reindex
    return self._ensure_type(super().reindex(**kwargs))
  File "/home/andrew/project/ch2/choochoo/py/env/lib/python3.7/site-packages/pandas/core/generic.py", line 4544, in reindex
    axes, level, limit, tolerance, method, fill_value, copy
  File "/home/andrew/project/ch2/choochoo/py/env/lib/python3.7/site-packages/pandas/core/frame.py", line 3744, in _reindex_axes
    index, method, copy, level, fill_value, limit, tolerance
  File "/home/andrew/project/ch2/choochoo/py/env/lib/python3.7/site-packages/pandas/core/frame.py", line 3760, in _reindex_index
    new_index, method=method, level=level, limit=limit, tolerance=tolerance
  File "/home/andrew/project/ch2/choochoo/py/env/lib/python3.7/site-packages/pandas/core/indexes/base.py", line 3145, in reindex
    target, method=method, limit=limit, tolerance=tolerance
  File "/home/andrew/project/ch2/choochoo/py/env/lib/python3.7/site-packages/pandas/core/indexes/base.py", line 2740, in get_indexer
    indexer = self._get_nearest_indexer(target, limit, tolerance)
  File "/home/andrew/project/ch2/choochoo/py/env/lib/python3.7/site-packages/pandas/core/indexes/base.py", line 2821, in _get_nearest_indexer
    left_distances = abs(self.values[left_indexer] - target)
numpy.core._exceptions.UFuncTypeError: ufunc 'subtract' cannot use operands with types dtype('<M8[ns]') and dtype('O')

This is a problem because it occurs in a larger dataset that I need to reindex. It used to work fine with earlier versions of Pandas (although I do not know which, sorry).

Expected Output

Expected output would be something like

>>> f2.reindex(i1)
Empty DataFrame
Columns: []
Index: [2016-06-26 14:27:26+00:00]

Output of pd.show_versions()

>>> pd.show_versions()

INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.4.final.0
python-bits      : 64
OS               : Linux
OS-release       : 4.12.14-lp151.28.36-default
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_GB.UTF-8
LOCALE           : en_GB.UTF-8

pandas           : 1.0.1
numpy            : 1.18.1
pytz             : 2019.3
dateutil         : 2.8.1
pip              : 20.0.2
setuptools       : 40.8.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.1
IPython          : 7.12.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : None
matplotlib       : 3.1.3
numexpr          : None
odfpy            : None
openpyxl         : 3.0.3
pandas_gbq       : None
pyarrow          : None
pytables         : None
pytest           : None
pyxlsb           : None
s3fs             : None
scipy            : 1.4.1
sqlalchemy       : 1.3.13
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
xlsxwriter       : None
numba            : None

[andrewcooke]

I just checked and the same error was present in 1.0.0 but not in 0.25.3 (which instead gives a warning about TZ related issues that I think is not directly relevant here?).

[jorisvandenbossche]

This doesn't raise an error anymore on master. But didn't check the 1.0.x branch yet. So we should check that, or otherwise find the commit on master that fixed it (and backport that), and add a test for it.

[TomAugspurger]

Is this fixed by #31511? That wasn't backported to 1.0.x.

[simonjayhawkins]

yes backporting #31511 will fix this. do we need to add a test?

[andrewcooke]

Thanks, so this will be in 1.0.2 I gather? :)

[mschroen]

yes backporting #31511 will fix this. do we need to add a test?

Can someone please tell how to "backport #31511" with pip? This reindex bug breaks all my workflows and unless 1.0.2 is not online I'd be happy to install a "backported version".