Unexpected behavior with binary operators and fill_value · Issue #12723 · pandas-dev/pandas (original) (raw)

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Description

From dask/dask#1063. fill_value doesn't seem to apply if the argument to a binary operator is a constant, but works fine for other arguments:

In [1]: import pandas as pd

In [2]: df = pd.DataFrame(range(10), columns=['foo'])

In [3]: df2 = df.copy()

In [4]: df2.iloc[0] = None

In [5]: df2.add(2, fill_value=0) Out[5]: foo 0 NaN 1 3.0 2 4.0 3 5.0 4 6.0 5 7.0 6 8.0 7 9.0 8 10.0 9 11.0

In [6]: df2.add(df, fill_value=0) Out[6]: foo 0 0.0 1 2.0 2 4.0 3 6.0 4 8.0 5 10.0 6 12.0 7 14.0 8 16.0 9 18.0

In [7]: pd.version Out[7]: u'0.18.0rc2+2.g19e40a0'

From the docstring I'd expect it to be equivalent to df2.fillna(0).add(2). If this is intended behavior, then the docstring should be updated to clarify this.