R help - Aug 2012 - Chopping a vector up into smaller vectors

Anyone got a neat way to chop a vector up into smaller subvectors?
This is what I have now, which seems inelegant:

chop <- function(v, counts) {
  stopifnot(sum(counts)==length(v))
  end <- cumsum(counts)
  beg <- c(1, 1+end[-length(end)])
  begend <- cbind(beg, end)
  apply(begend, 1, function(x) v[x[1]:x[2]])
}
  
> chop(9:1, c(3,2,4))
[[1]]
[1] 9 8 7

[[2]]
[1] 6 5

[[3]]
[1] 4 3 2 1

Hi Stephen,
how about this:

chop<-function(x,counts){
 stopifnot(sum(counts)==length(x))
 split(9:1,unlist(mapply(rep,seq_along(counts),counts)))
}
chop(9:1,c(3,2,4))

cheers

Am 02.08.2012 12:29, schrieb Stephen Eglen:
> Anyone got a neat way to chop a vector up into smaller subvectors?
> This is what I have now, which seems inelegant:
> 
> chop <- function(v, counts) {
>   stopifnot(sum(counts)==length(v))
>   end <- cumsum(counts)
>   beg <- c(1, 1+end[-length(end)])
>   begend <- cbind(beg, end)
>   apply(begend, 1, function(x) v[x[1]:x[2]])
> }
>   
> 
>> chop(9:1, c(3,2,4))
> [[1]]
> [1] 9 8 7
> 
> [[2]]
> [1] 6 5
> 
> [[3]]
> [1] 4 3 2 1
> 
> ______________________________________________
> R-help at r-project.org mailing list
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 

-- 
Eik Vettorazzi

Department of Medical Biometry and Epidemiology
University Medical Center Hamburg-Eppendorf

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Hi

one of possible options

f<- function(x, parts) split(x,rep(1:length(parts),parts))
f(9:1, c(3,2,4))
$`1`
[1] 9 8 7

$`2`
[1] 6 5

$`3`
[1] 4 3 2 1

You can also check if your parts vector agrees with x vector, if you want.

Regards
Petr

> 
> Anyone got a neat way to chop a vector up into smaller subvectors?
> This is what I have now, which seems inelegant:
> 
> chop <- function(v, counts) {
>   stopifnot(sum(counts)==length(v))
>   end <- cumsum(counts)
>   beg <- c(1, 1+end[-length(end)])
>   begend <- cbind(beg, end)
>   apply(begend, 1, function(x) v[x[1]:x[2]])
> }
> 
> 
> > chop(9:1, c(3,2,4))
> [[1]]
> [1] 9 8 7
> 
> [[2]]
> [1] 6 5
> 
> [[3]]
> [1] 4 3 2 1
> 
> ______________________________________________
> 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.