Try this:
> aggregate(dat["A"], dat["Group"], mean)
Group A
1 1 0.4944810
2 2 0.4765412
3 3 0.4521068
4 4 0.4989000
On Sat, May 9, 2009 at 8:14 AM, Gavin Simpson <gavin.simp...@ucl.ac.uk> wrote:
> Hi,
>
> I find it a bit annoying that aggregate.default forces the returned
> object to loose the 'name' of the variable aggregated, replacing it with
> 'x'.
>
> A brief example:
>
>> dat <- data.frame(A = runif(100), B = rnorm(100),
> + Group = gl(4, 25))
>> with(dat, aggregate(A, by = list(Group = Group), FUN = mean))
> Group x
> 1 1 0.6523228
> 2 2 0.4544317
> 3 3 0.4619624
> 4 4 0.4703156
>
> This arises because aggregate default has:
>
> function (x, ...)
> {
> if (is.ts(x))
> aggregate.ts(as.ts(x), ...)
> else aggregate.data.frame(as.data.frame(x), ...)
> }
>
> which recasts x as a data frame, but doesn't make any effort to supply a
> name. Can we do a better job of supplying a useful name?
>
> My first attempt is:
>
> aggregate.default <- function(x, ...) {
> if (is.ts(x))
> aggregate.ts(as.ts(x), ...)
> else {
> nam <- deparse(substitute(x))
> x <- as.data.frame(x)
> names(x) <- nam
> aggregate.data.frame(x, ...)
> }
> }
>
> Which works for the brief example above:
>
>> with(dat, aggregate(A, by = list(Group = Group), FUN = mean))
> Group A
> 1 1 0.4269715
> 2 2 0.5479352
> 3 3 0.5091543
> 4 4 0.4926412
>
> However, it fails make check-all because examples have relied on
> returned object having 'x'. I also note that this might have the
> annoying side effect of producing odd names if we use the following
> incantation:
>
>> res <- aggregate(dat$A, by = list(Group = dat$Group), FUN = mean)
>> str(res)
> 'data.frame': 4 obs. of 2 variables:
> $ Group: Factor w/ 4 levels "1","2","3","4": 1 2 3 4
> $ dat$A: num 0.427 0.548 0.509 0.493
>> res$dat$A
> Error in res$dat$A : $ operator is invalid for atomic vectors
>> res$`dat$A`
> [1] 0.4269715 0.5479352 0.5091543 0.4926412
>
> Is there a way of coming up with a better way to name the aggregated
> variable? Would a change of this kind be something R Core would consider
> making to aggregate.default if a good solution is found?
>
> Thanks in advance,
>
> G
> --
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> Dr. Gavin Simpson [t] +44 (0)20 7679 0522
> ECRC, UCL Geography, [f] +44 (0)20 7679 0565
> Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk
> Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/
> UK. WC1E 6BT. [w] http://www.freshwaters.org.uk
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>
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