[R] Aggregrate function

[Christos Hatzis]

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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