Question

Considering a test dataset,

dat=data.frame(name=c('A','A','B','C','C','C'),val=c(1,1,2,2,3,2))

name val
A   1
A   1
B   2
C   2
C   3
C   2

What would be the most efficient way to get this output

name val
A   1
A-1   1
B   2
C   2
C-1   3
C-2   2

So, just marking the duplicates with a custom identifier.
I could think of marking them with an common identifier using paste(dat[which(duplicated(dat$name)),1],"-1",sep=''), but this will just put “-1” in front of all the duplicated ones. I want if the item appears for the 3rd time, mark it with “-2” and so on.

Cheers

Answer 1

Using make.unique:

transform(dat,name=make.unique(as.character(name),sep="-"))
  name val
1    A   1
2  A-1   1
3    B   2
4    C   2
5  C-1   3
6  C-2   2