Merging two columns into one in R

Question

I have the following data frame, and am trying to merge the two columns into one, while replacing NA\'s with the numeric values.

ID    A     B
1         


        

Answer 1

This question's been around for a while, but just to add another possible approach that does not depend on any libraries:

df$new = t(df[-1])[!is.na(t(df[-1]))]

#   ID  A  B new
# 1  1  3 NA   3
# 2  2 NA  2   2
# 3  3 NA  4   4
# 4  4  1 NA   1