Try this:
> aggregate(myframe[4], myframe[1:3], min)
factor1 factor2 factor3 y
1 1 a x 1
2 2 a x 9
3 1 b x 5
4 2 b x 13
5 1 a y 3
6 2 a y 11
7 1 b y 7
8 2 b y 15
On Mon, Jan 11, 2010 at 7:58 PM, JustinNabble
<justinmmcgr...@hotmail.com> wrote:
>
> I'd like to get a long data set of minimum values from groups in another data
> set.
> The following almost does what I want. (Note, I'm using the word factor
> differently from it's meaning in R; bad choice of words)
>
> myframe = data.frame(factor1 = rep(1:2,each=8), factor2 =
> rep(c("a","b"),each=4, times=2), factor3 = rep(c("x","y"),each=2, times=4),
> y=1:16)
> attach(myframe)
> minimums = by(y, list(factor1, factor2,factor3), min)
> detach(myframe)
>
> The problem is that "minimums" is object of class "by", which looks like
> some kind of array with the number of dimension equal to the number of
> factors. I just want two dimensions though, with factors in columns. I can't
> figure out how to reformat it to something like this:
>
> factor1 factor2 factor2 y
> 1 a x 1
> 2 a x 9
> 1 b x 5
> ...
>
> I could make nested for loops, but I'd like something that will work for an
> arbitrary number of factors. I've seen some functions that will rearrange
> data (e.g. reshape), but they all seem to require a data.frame to start
> with.
> --
> View this message in context:
> http://n4.nabble.com/How-to-get-minimum-value-by-group-tp1011745p1011745.html
> Sent from the R help mailing list archive at Nabble.com.
>
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