[R] Aggregrate function

[Christos Hatzis]

This requires a small modification to use which instead of which.max that
returns only the first maximum:

do.call("rbind", lapply(split(xveg, xveg$loc), function(x) x[which(x$tot ==
max(x$tot)), ]))

     loc sp tot
L1    L1  b  60
L2.5  L2  d  25
L2.7  L2  e  25
L3    L3  b  68 

-Christos

> -----Original Message-----
> From: Monica Pisica [mailto:pisicandru at hotmail.com] 
> Sent: Thursday, February 12, 2009 4:35 PM
> To: christos.hatzis at nuverabio.com; R help project; 
> markleeds at verizon.net
> Subject: RE: [R] Aggregrate function
> 
> 
> 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.
> >> 
> >> ______________________________________________
> >> R-help at r-project.org mailing list
> >> 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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