Question

Say I have a dataframe

source <- data.frame(ID=c(1,2), COUNT=c(3,4))

that looks like this:

  ID COUNT
1  1     3
2  2     4  

I’d like to transform this into a dataframe that has COUNT records for each ID, with a new unique ITEMID, like this

  ITEMID SOURCEID
1      1        1
2      2        1
3      3        1
4      4        2
5      5        2
6      6        2
7      7        2

I can do it with a for loop, but am looking to learn how to do this with apply type functions

Answer 1

No need for apply functions:

orig <- data.frame(ID=1:2,COUNT=3:4)
new <- data.frame(ITEMID=seq(sum(orig$COUNT)), SOURCEID=rep(orig$ID,times=orig$COUNT))
new
  ITEMID SOURCEID
1      1        1
2      2        1
3      3        1
4      4        2
5      5        2
6      6        2
7      7        2