[R] select the last row by id group

[Gabor Grothendieck]

Try this:

score[tapply(rownames(score), score$id, tail, 1),]


On 6/12/06, Tony Chu <gatony at gmail.com> wrote:
>  Dear R users:
>
>  I have a small test dataframe as the follows :
>
> math = c(80,75,70,65,65,70)
> reading = c(65,70,88,NA,90,NA)
> id = c('001','001','001','002','003','003')
> score = data.frame(id, reading, math)
>
> > score
>   id reading math
> 1 001      65   80
> 2 001      70   75
> 3 001      88   70
> 4 002      NA   65
> 5 003      90    65
> 6 003      NA   70
>
>  Could someone advise me tips about how to select the last row from
> each id group of 001, 002, & 003?
>
> In other words, the rows I need are :
>
>   id reading math
> 3 001      88   70
> 4 002      NA   65
> 6 003      NA   70
>
>  I tried function sebset but could not go very far. Thanks !
>
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