Does this do it for you?
> x <- read.table(textConnection(" id day k
+ 56 -1 566
+ 63 -1 680
+ 73 -1 773
+ 56 2 298
+ 63 2 273"), header=TRUE)
> x$percent <- ave(x$k, list(x$id), FUN=function(.data){
+ (.data - .data[1]) / .data[1] * 100
+ })
>
> x
id day k percent
1 56 -1 566 0.00000
2 63 -1 680 0.00000
3 73 -1 773 0.00000
4 56 2 298 -47.34982
5 63 2 273 -59.85294
>
On Nov 30, 2007 8:44 PM, Judith Flores <[EMAIL PROTECTED]> wrote:
> Sorry about that, it was sent by accident.
>
> I have a data frame that looks something like this:
>
> id day k
> 56 -1 566
> 63 -1 680
> 73 -1 773
> 56 2 298
> 63 2 273
>
> Of course, it is a very simplified version of the
> real data frame I am working on. I need to add another
> column that would represent a percent change in k from
> day -1, by id. I put only two ids at day 2 to
> emphasize the fact that after day -1 some subjects
> won't be on the data frame any more.
>
> I tried something like this:
>
> pck<-by(dat,dat[,c("id","day")], function(x) {
> pc<-((x$k-x$k[x$day==-1])/x$k[x$day==-1])*100
> })
> but it didn't work.
>
> Then I tried:
>
> for(i in dat$id) {
>
> for(s in dat$day) {
> pc<-((dat$k[dat$id==i &
> dat$day==s]-dat$k[dat$id==i &
> dat$day==-1])/dat$k[dat$id==i & dat$day==-1])*100
> }
> }
> without success.
>
> I am sure it is very simple to do, but I would
> appreciate any hints.
>
> Thank you,
>
> Judith
>
>
>
>
>
>
>
> ____________________________________________________________________________________
> Be a better pen pal.
>
> ______________________________________________
> R-help@r-project.org mailing list
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
--
Jim Holtman
Cincinnati, OH
+1 513 646 9390
What is the problem you are trying to solve?
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