In [7]: df Out[7]: 0 1 0 NaN NaN 1 -0.494375 0.570994 2 NaN NaN 3 1.876360 -0.229738 4 NaN NaN In [8]: df.fillna(0) Out[8]: 0 1 0 0.000000 0.000000 1 -0.494375 0.570994 2 0.000000 0.000000 3 1.876360 -0.229738 4 0.000000 0.000000
In [12]: df[1].fillna(0, inplace=True) Out[12]: 0 0.000000 1 0.570994 2 0.000000 3 -0.229738 4 0.000000 Name: 1 In [13]: df Out[13]: 0 1 0 NaN 0.000000 1 -0.494375 0.570994 2 NaN 0.000000 3 1.876360 -0.229738 4 NaN 0.000000