Python pandas apply function if a column value is not NULL

Question

I have a dataframe (in Python 2.7, pandas 0.15.0):

df=
       A    B               C
0    NaN   11             NaN
1    two  NaN  [\'foo\', \'bar\']
2  three   3         


        

Answer 1

Try...

df['a'] = df['a'].apply(lambda x: x.replace(',','\,') if x != None else x)

this example just adds an escape character to a comma if the value is not None