give unique id based on other columns

Question

I have data like this

a1  a2   a3
1   22   44
1   22   33
2   44    3
2   55   5
3   22   7

I like to give unique ids based on the a1 and a2 combination:

a1  a2   a3   id
1   22   44    1
1   22   33    1
2   44    3    2
2   55   5     3
3   22   7     4

Thanks.

score 1 · Accepted Answer · answered Dec 18 '13 at 19:16

1

The most straightforward way in base R is to probably use factor:

> as.integer(factor(with(mydf, paste(a1, a2))))
[1] 1 1 2 3 4

answered Dec 18 '13 at 19:16

1 Answers1