In pandas, what does the na_action parameter to Series.map do -

when using series.map, na_action do? docs unclear , have not come example in results affected parameter.

although explanation in documentation pretty clear, it's hard see what's going on if you're using numeric functions take nans input , return them nan. else hasn't read docs, if na_action='ignore' na values not passed mapping function, if na_action=none (the default) will.

here's trivial example showing difference:

import pandas pd import numpy np  s = pd.series([1, 2, 3, np.nan])  s2 = s.map(lambda x: 'this string {}'.format(x), na_action=none)  0    string 1.0 1    string 2.0 2    string 3.0 3    string nan dtype: object  s3 = s.map(lambda x: 'this string {}'.format(x), na_action='ignore')  0    string 1.0 1    string 2.0 2    string 3.0 3                     nan dtype: object 

if have better example own analysis should consider creating issue on pandas repo, in order improve documentation , others understand.