[R] Aggregrate function

[Monica Pisica]

Hi, 
 
Thanks for the solution. Mark Leeds sent me privately a very similar solution. My next question to him was:
 
Suppose that for a certain location 2 species have the same maximum total ... (there are ties in the data for a particular location). How do i get all species that have that max. total??
 
For this case i have changed the tot as follows:
 
tot <-  c(20, 60, 40, 15, 25, 15, 25, 20, 68, 32)
 
His sollution is (and does work):
 
temp <- lapply(split(xveg,loc), function(.df) {
  maxindices <- which(.df$tot == .df$tot[which.max(.df$tot)])
  data.frame(loc=.df$loc[1],sp=paste(.df$sp[maxindices],collapse=","),tot=max(.df$tot))
})

result <- do.call(rbind,temp)
print(result)
 
Thanks so much again,
 
Monica 
 

 
> From: christos.hatzis at nuverabio.com
> To: pisicandru at hotmail.com; r-help at r-project.org
> Subject: RE: [R] Aggregrate function
> Date: Thu, 12 Feb 2009 15:56:38 -0500
> 
> 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-bounces at r-project.org 
>> [mailto:r-help-bounces 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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>> https://stat.ethz.ch/mailman/listinfo/r-help
>> 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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