Let's say we have a 6*4 data frame in which third and fourth column contain missing value
1 2 3 L1
4 5 6 L2
7 8 9 L3
4 8 NaN NaN
2 3 4 5
7 9 NaN NaN
I'd like to fill the missing value by looking at another row that has the same value for the first column. So, in the end, I should have:
1 2 3 L1
4 5 6 L2
7 8 9 L3
4 8 6 L2 <- Taken from 4 5 6 L2 row
2 3 4 L4
7 9 9 L3 <- Taken from 7 8 9 L3 row
How can we do it with Pandas in the fastest way possible?