[FIXED] How to conditionally replace values in a pandas dataframe column with values from another column

Issue

I know this type of question has been asked many times before. With the answers provided I am not able to move beyond this point.

I have a dataframe named areas. I want have a new column which takes the values from column area1 unless the value is NaN then the value must be taken from area2.

area1 area2
NaN   100
NaN   101
NaN   102
A     103
B     104
C     105

I have tried a bunch of things but am stuck. The last thing I tried was.

areas['area3'] = np.where(areas['area1'].isnan, areas['areas2'])

Help would be very much appreciated

Solution

You missing the 2nd condition and function name should be isna

areas['area3'] = np.where(areas['area1'].isna(), areas['area2'], areas['area1'])

Answered By - BENY