A bit convolulted but it works
library(reshape2)
yy <- melt(dat)
zz <- cast(yy, id.var ~ variable, min)
zz[,2]
--- On Tue, 5/17/11, Downey, Patrick <pdow...@urban.org> wrote:
> From: Downey, Patrick <pdow...@urban.org>
> Subject: [R] Minimum value by ID
> To: r-help@r-project.org
> Received: Tuesday, May 17, 2011, 9:44 AM
> Hello,
>
> I have a longitudinal dataset where each individual has a
> different number
> of entries. Thus, it is of the following structure:
>
> x <- runif(12)
> id.var <-
> factor(c(rep("D1",4),rep("D2",2),rep("D3",3),rep("D4",3)))
> dat <- as.data.frame(x)
> dat$id.var <- id.var
> dat
>
> > dat
> x
> id.var
> 1 0.9611269 D1
> 2 0.6738606 D1
> 3 0.9724301 D1
> 4 0.9787778 D1
> 5 0.2468355 D2
> 6 0.7031734 D2
> 7 0.2458727 D3
> 8 0.8439799 D3
> 9 0.5223196 D3
> 10 0.6930475 D4
> 11 0.8887677 D4
> 12 0.5483756 D4
>
> I want to create a vector with length equal to the number
> of unique id.var
> and which has the minimum value for each id.var. That is, I
> want a vector
> which holds the minimum value for each person in my
> dataset.
>
> The following works, but I'm sure there is something more
> efficient. I
> would assume there is a function for this, but couldn't
> find anything.
>
> id <- levels(id.var)
> min <- rep(0,length(id))
> for(i in 1:length(id)){
> min[i] <- min(dat$x[dat$id.var==id[i]])
> }
> min
>
> > min
> [1] 0.6738606 0.2468355 0.2458727 0.5483756
>
> Thank you in advance,
> Mitch
>
> ______________________________________________
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> mailing list
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>
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