# [R] Aggregrate function

David Winsemius dwinsemius at comcast.net
Thu Feb 12 23:52:35 CET 2009

```aggregate and by are convenience functions of tapply.

Consider this alternate solution:

xveg[which(xveg\$tot %in% with(xveg, tapply(tot, loc, max))),"sp"]

It uses tapply to find the maximums by loc(ations) and then to goes
back into xveg to find the corresponding sp(ecies).  You should do
testing to see whether the handling of ties agrees with your needs.

--
David Winsemius

On Feb 12, 2:56 pm, "Christos Hatzis" <christos.hat... at nuverabio.com>
wrote:
> I don't have an easy solution with aggregate, because the function in
> aggregate needs to return a scalar.
> But the following should work:
>
> do.call("rbind", lapply(split(xveg, xveg\$loc), function(x)
> x[which.max(x\$tot), ]))
>
>    loc sp tot
> L1  L1  b  60
> L2  L2  e  30
> L3  L3  b  68
>
> -Christos
>
>
>
> > -----Original Message-----
> > From: r-help-boun... at r-project.org
> > [mailto:r-help-boun... at r-project.org] On Behalf Of Monica Pisica
> > Sent: Thursday, February 12, 2009 1:58 PM
> > To: R help project
> > Subject: [R] Aggregrate function
>
> > Hi,
>
> > I have to recognize that i don't fully understand the
> > aggregate function, but i think it should help me with what i
> > want to do.
>
> > xveg is a data.frame with location, species, and total for
> > the species. Each location is repeated, once for every
> > species present at that location. For each location i want to
> > find out which species has the maximum total ... so i've
> > tried different ways to do it using aggregate.
>
> > loc <- c(rep("L1", 3), rep("L2", 5), rep("L3", 2)) sp <-
> > c("a", "b", "c", "a", "d", "b", "e", "c", "b", "d") tot <-
> > c(20, 60, 40, 15, 25, 10, 30, 20, 68, 32) xveg <-
> > data.frame(loc, sp, tot)
>
> > result desired:
>
> > L1   b
> > L2   e
> > L3   b
>
> > sp_maj <- aggregate(xveg[,2], list(xveg[,1], function(x)
> > levels(x)[which.max(table(x))])
>
> > This is wrong because it gives the first species name in each
> > level of location, so i get a, a, b, as species instead of b, e, b.
>
> > I've tried other few aggregate commands, all with wrong results.
>
> > I will appreciate any help,
>
> > Thanks,
>
> > Monica
>
> > _________________________________________________________________
>
> >  the go.
>
> > ______________________________________________
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