column-wise fillna with Series/dict NotImplemented

[hayd]

As per discussion on this SO question is NotImplementedError.

Solution/workaround is to transpose do transpose? This is used elsewhere in DataFrame.fillna method. just raise if inplace?

cc @cpcloud

In [9]: df = pd.DataFrame([[np.nan, np.nan], [np.nan, 4], [5, 6]], columns=list('AB'))

In [10]: df
Out[10]:
    A   B
0 NaN NaN
1 NaN   4
2   5   6

In [11]: df.mean(0)
Out[11]:
A    5
B    5
dtype: float64

In [12]: df.fillna(df.mean())
Out[12]:
   A  B
0  5  5
1  5  4
2  5  6

In [13]: df.mean(1)
Out[13]:
0    NaN
1    4.0
2    5.5
dtype: float64

In [14]: df.fillna(df.mean(1), axis=1)
---------------------------------------------------------------------------
NotImplementedError                       Traceback (most recent call last)
<ipython-input-14-aecc493431e2> in <module>()
----> 1 df.fillna(df.mean(1), axis=1)

/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pandas/core/frame.pyc in fillna(self, value, method, axis, inplace, limit, downcast)
   3452             if isinstance(value, (dict, Series)):
   3453                 if axis == 1:
-> 3454                     raise NotImplementedError('Currently only can fill '
   3455                                               'with dict/Series column '
   3456                                               'by column')

NotImplementedError: Currently only can fill with dict/Series column by column

[jreback]

this is pretty straightforward after merging in series subclass NDFrame. This has to deal with possible dtype changes when doing column wise (which I think its not-implemented)

[jorisvandenbossche]

Came up again at SO

[aileronajay]

@jreback @jorisvandenbossche is this implemented yet? I was trying to do this result.fillna(result.mean(axis=1), axis =1 ) and got the same exception

[jreback]

issue is open

[aspiringguru]

my simple/crude workaround below. curious why this issue is still open in 2018.

colnames = list(df)

for colname in colnames:
df[colname].fillna(method='bfill', inplace=True)

[jorisvandenbossche]

curious why this issue is still open in 2018.

Because nobody made the effort to implement it. But you are welcome to do so.

[malbahrani]

Faced the same issue. It is worth mentioning here, @hayd solution posted in StackOverflow

Thanks for the workaround Andy!

[aadarshsingh191198]

This isn't implemented even in the latest version of pandas (v2.0.1). Can we reopen this issue, please?

[aftersought]

To confirm, in my usage ffill(axis=1, inplace=True) works as long as all dtypes of the columns are the same; I get NotImplemented error if they have mixed dtypes.

[ShivnarenSrinivasan]

I see this is still an open issue
Not sure if I will be able to implement this, but assigning to myself to build on top of previous PR attempts.

take

[kdebrab]

Solution/workaround is to do transpose?

We actually used transpose (i.e., df.T.fillna(df.mean(1)).T), but it proved to be really horrendous with regard to performance. This performance issue happens especially when the index of df is (much) longer than the number of columns. We solved it by using apply instead:

df_mean = df.mean(1)
df.apply(lambda col: col.fillna(df_mean))