try this:
> x <- read.table('clipboard')
> x
V1 V2
1 1 A
2 2 A
3 3 A
4 4 A
5 5 B
6 6 B
7 7 B
8 8 C
9 9 C
10 10 C
11 11 C
12 12 C
> x$ID <- ave(x$V1, x$V2, FUN = function(a)seq(length(a)))
> x
V1 V2 ID
1 1 A 1
2 2 A 2
3 3 A 3
4 4 A 4
5 5 B 1
6 6 B 2
7 7 B 3
8 8 C 1
9 9 C 2
10 10 C 3
11 11 C 4
12 12 C 5
>
On Wed, Sep 21, 2011 at 11:02 PM, Toni Pitcher <toni.pitc...@otago.ac.nz> wrote:
> Hi R Users
>
> I am hoping someone might be able to give some pointers on alternative code
> to the for loop described below.
>
> I have a dataset which is ordered by subject ID and date, what I would like
> to do is create a new variable that numbers the entries for each person (e.g.
> 1,2,3,....)
>
> As an example if we have subjects A, B and C all with multiple entries (have
> excluded date variable for simplicity), the for loop below achieves the
> desired result, however my dataset is big (1 million + observations) and the
> for loop is slow. Is there a more efficient way of getting to the desired
> result?
>
> Many thanks in advance
>
> Toni
>
>
> A <- data.frame(ID=c('A','A','A','A','B','B','B', 'C','C','C','C','C'))
>
> ID
> 1 A
> 2 A
> 3 A
> 4 A
> 5 B
> 6 B
> 7 B
> 8 C
> 9 C
> 10 C
> 11 C
> 12 C
>
>
> A$Session_ID <- 0
> previous_ID <- ''
> current_index <- 1
> for ( i in seq(1,nrow(A)) )
> {
> if (A$ID[i] != previous_ID)
> {current_index <- 1}
> A$Session_ID[i] <- current_index
> previous_ID <- A$ID[i]
> current_index <- current_index + 1
> }
>
>
>
> ID Session_ID
> 1 A 1
> 2 A 2
> 3 A 3
> 4 A 4
> 5 B 1
> 6 B 2
> 7 B 3
> 8 C 1
> 9 C 2
> 10 C 3
> 11 C 4
> 12 C 5
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
--
Jim Holtman
Data Munger Guru
What is the problem that you are trying to solve?
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and provide commented, minimal, self-contained, reproducible code.
