I have a dataframe:
A B
1 NaN
2 3
4 NaN
5 NaN
6 7
I want to create a new column C containing the value from B that aren't NaN, otherwise the values from A. This would be a simple matter in Excel; is it easy in Pandas?
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1 Answer
Yes, it's simple. Use pandas.Series.where:
df['C'] = df['A'].where(df['B'].isna(), df['B'])
Output:
>>> df
A B C
0 1 NaN 1
1 2 3.0 3
2 4 NaN 4
3 5 NaN 5
4 6 7.0 7
A bit cleaner:
df.C = df.A.where(df.B.isna(), df.B)
Alternatively:
df.C = df.B.where(df.B.notna(), df.A)