[R] Aggregrate function
dwinsemius at comcast.net
Fri Feb 13 06:13:08 CET 2009
I realized later that the which might not be necessary (and in
addition was reminded privately). The %in% function returns a logical
vector which works just as well with matrix or dataframe indexing as
the numeric vector returned by which.
On Feb 12, 2009, at 5:52 PM, David Winsemius wrote:
> aggregate and by are convenience functions of tapply.
> Consider this alternate solution:
> xveg[which(xveg$tot %in% with(xveg, tapply(tot, loc, max))),"sp"]
> It uses tapply to find the maximums by loc(ations) and then to goes
> back into xveg to find the corresponding sp(ecies). You should do
> testing to see whether the handling of ties agrees with your needs.
> David Winsemius
> On Feb 12, 2:56 pm, "Christos Hatzis" <christos.hat... at nuverabio.com>
>> I don't have an easy solution with aggregate, because the function in
>> aggregate needs to return a scalar.
>> But the following should work:
>> do.call("rbind", lapply(split(xveg, xveg$loc), function(x)
>> x[which.max(x$tot), ]))
>> loc sp tot
>> L1 L1 b 60
>> L2 L2 e 30
>> L3 L3 b 68
>>> -----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
>>> 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)
>>> 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,
>>> the go.
>>> R-h... at r-project.org mailing list
>>> PLEASE do read the posting guide
>>> and provide commented, minimal, self-contained, reproducible code.
>> R-h... at r-project.org mailing listhttps://stat.ethz.ch/mailman/
>> PLEASE do read the posting guidehttp://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
> R-help at r-project.org mailing list
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
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