pandas combine two strings ignore nan values

Question

I have two columns with strings. I would like to combine them and ignore nan values. Such that:

ColA, Colb, ColA+ColB str   str    strstr str   nan    str nan   str    str 

I tried df['ColA+ColB'] = df['ColA'] + df['ColB'] but that creates a nan value if either column is nan. I've also thought about using concat.

I suppose I could just go with that, and then use some df.ColA+ColB[df[ColA] = nan] = df[ColA] but that seems like quite the workaround.

Answer 1

Call fillna and pass an empty str as the fill value and then sum with param axis=1:

In [3]: df = pd.DataFrame({'a':['asd',np.NaN,'asdsa'], 'b':['asdas','asdas',np.NaN]}) df  Out[3]:        a      b 0    asd  asdas 1    NaN  asdas 2  asdsa    NaN  In [7]: df['a+b'] = df.fillna('').sum(axis=1) df  Out[7]:        a      b       a+b 0    asd  asdas  asdasdas 1    NaN  asdas     asdas 2  asdsa    NaN     asdsa 

Answer 2

You could fill the NaN with an empty string:

df['ColA+ColB'] = df['ColA'].fillna('') + df['ColB'].fillna('')