[R] Numbering entries for each subject

[jim holtman]

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.pitcher at 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
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>



-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?