# [R] sum of grouped elements of vector

Jim Lemon drjimlemon at gmail.com
Fri Jan 23 10:14:02 CET 2015

```Hi Kathryn,
I think this might do the trick:

make_group_sums<-function(x,maxgroups) {
lenx<-length(x)
runlengths<-sample(1:lenx,1)
for(i in 2:(maxgroups-1)) {
lenx<-lenx-runlengths[i-1]
runlengths[i]<-ifelse(lenx,sample(1:lenx,1),0)
}
runlengths[maxgroups]<-length(x)-sum(runlengths)
groups<-rep(1:maxgroups,runlengths)
groupsums<-by(x,groups,sum)
return(as.vector(groupsums))
}

Jim

On Fri, Jan 23, 2015 at 7:45 PM, Kathryn Lord
<kathryn.lord2000 at gmail.com> wrote:
> Dear R users,
>
> I have a quick quesiton.
>
> Here is a vector "a".
>
> a<- c(1,2,3,4,5,6,7,8).
>
> (In fact, I have a huge vector.)
>
>
> With "a", I'd like to create new vectors, for example,
>
> new1 = (1+2, 3, 4+5+6, 7+8)
> new2 = (1, 2+3+4+5+6+7, 8)
> new3 = (1+2+3+4+5+6+7, 8)
>
>
> How could I make the above vectors using R?
>
>
> Any suggestion will be greatly appreciated.
>
> Best,
>
> Kathryn Lord
>
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>
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