Question

How can I combind two columns in the same data frame into one column, a simple example would be:

a <- data.frame(id = 1:3, v1 = c('a', NA, NA), v2 = c(NA, 'b', 'c'))
a
  id  v1   v2
   1  a   <NA>
   2 <NA>  b
   3 <NA>  c

And the output I need would be look like this:

a
  id  v1   v2   v3
   1  a   <NA>   a
   2 <NA>  b     b
   3 <NA>  c     c

I found a similar post join matching columns in a data.frame or data.table, but I can not figure it out with my own case, please help, thanks

Answer 1

Hmm, ifelse() maybe?

> a <- data.frame(id = 1:3, v1 = c('a', NA, NA), v2 = c(NA, 'b', 'c'),
                  stringsAsFactors=FALSE)
> a$v3 <- ifelse(is.na(a$v1), a$v2, a$v1)
> a
  id   v1   v2 v3
1  1    a <NA>  a
2  2 <NA>    b  b
3  3 <NA>    c  c