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BUG/ER: misleading results when filling with a reversed index #4484

jreback opened this issue Aug 6, 2013 · 1 comment


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commented Aug 6, 2013

created by @prossahl

Reversing an index and forward filling succeeds but produces misleading data:

>>> dr = pd.date_range('2013-08-01', periods=6, freq='B')
>>> df = pd.DataFrame(np.random.randn(6,1), index=dr, columns=list('A'))
>>> df['A'][3] = np.nan
>>> df.reindex(df.index[::-1], method='ffill')
2013-08-08  2.127302
2013-08-07       NaN
2013-08-06       NaN
2013-08-05       NaN
2013-08-02       NaN
2013-08-01       NaN

This change enforces "monotocity" (well actually weakly increasing) and causes a ValueError to be raised.


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commented Sep 15, 2013

Closed by #4642

@jtratner jtratner closed this Sep 15, 2013

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