create an ID column by its natural order

Question

I have a dataset like this

df=data.frame(subject= c(rep(1001, 3), rep(732, 2),rep(966,4)))

I wish to create an ID column so that the output could look like this

  subject id
1    1001  1
2    1001  1
3    1001  1
4     732  2
5     732  2
6     966  3
7     966  3
8     966  3
9     966  3

I used the code df$id <- as.numeric(as.factor(df$subject)) , but it gave me an id column ordered by the subject number like this

  subject id
1    1001  3
2    1001  3
3    1001  3
4     732  1
5     732  1
6     966  2
7     966  2
8     966  2
9     966  2

does anyone know how to make the id column with its natural order?

@rawr, why do you so often answer questions as a comment and not write a full answer? I see you do this a lot (700+ comments for only 75 answers) and I find it a bit counter productive for everyone. — flodel, Aug 06 '14 at 00:42

score 2 · Answer 1 · answered Aug 06 '14 at 08:58

2

Simply coping rawr's comment to get the question closed (I'm happy to delete this answer if rawr post an answer)

df=data.frame(subject= c(rep(1001, 3), rep(732, 2),rep(966,4)))
df
  subject id
1    1001  1
2    1001  1
3    1001  1
4     732  2
5     732  2
6     966  3
7     966  3
8     966  3
9     966  3

answered Aug 06 '14 at 08:58

Eric Fail

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+1 have some credit for taking the time to answer. And for attributing the source of your answer. – Simon O'Hanlon Aug 06 '14 at 09:02
@SimonO'Hanlon, Well, thank you! – Eric Fail Aug 07 '14 at 08:46

create an ID column by its natural order

1 Answers1