bartjoosen wrote:
> How about:
>
> tapply(dat$x1,dat$subject,function(x) cumsum(x))
> which gives you a list for each subject.
>
> this can be converted to a vector:
> do.call("c",tapply(dat$x1,dat$subject,function(x) cumsum(x)))
>
> So if your data frame is ordered for your subjects:
>
> cbind(your.data.frame,do.call("c",tapply(dat$x1,dat$subject,function(x)
> cumsum(x))))
>
>
Sounds like a job for the eternally overlookked ave() function:
with(dat, ave(x1, subject, cumsum))
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