First column name with non null value by row pandas

Question

I want know the first year with incoming revenue for various projects.

Given the following, dataframe:

ID  Y1      Y2      Y3
0   NaN     8       4
1         


        

Answer 1

You can apply first_valid_index to each row in the dataframe using a lambda expression with axis=1 to specify rows.

>>> df.apply(lambda row: row.first_valid_index(), axis=1)
ID
0      Y2
1      Y3
2    None
3      Y1
dtype: object

To apply it to your dataframe:

df = df.assign(first = df.apply(lambda row: row.first_valid_index(), axis=1))

>>> df
    Y1  Y2  Y3 first
ID                  
0  NaN   8   4    Y2
1  NaN NaN   1    Y3
2  NaN NaN NaN  None
3    5   3 NaN    Y1