Changing value of data frame based on another data frame

Question

Again I need your help for a maybe easy question that is not clear for a starter R user.

I need to manipulate a dataframe to substitute NA values by \"

Answer 1

It's actually quite simple to do this without a for loop: if your data frames are A and B, then the command would be

A[A == -3] = B[A == -3]

In other words: for all the indices of A that have value -3, assign the values of B at the corresponding indices.