gistfile1.r

> d = data.frame(mediumid=c(4,4,4,5,5,6,7,5))
> d
  mediumid
1        4
2        4
3        4
4        5
5        5
6        6
7        7
8        5
> d$medium = factor(d$mediumid, levels=c(4,5,6,7), labels=c("vk", "nrc", "trw", "tel"))
> d
  mediumid medium
1        4     vk
2        4     vk
3        4     vk
4        5    nrc
5        5    nrc
6        6    trw
7        7    tel
8        5    nrc