[R] sum variable as long condition is true

[John Kane]

aggregate(c$a, list(b=b), sum)  

--- marcg <mdgi at gmx.ch> wrote:

> Hello R
> 
> For expierienced user, the following problem will be
> easy to solve:
> 
> a<-c(0,1,0,1,0,2,3,4,3,2)
> b<-c(3,3,3,4,4,4,7,7,7,10)
> c<-data.frame(a,b)
> 
> Data Frame c contains tow colums. I would like to
> sum up all values in a as long as b stays the same:
> 
> sum(a[which(b==1)])
> 
> does this, but i have to manually put in b
> 
> then i tryied st like this, but i canno't save it
> properly
> 
> for (i in 0:max(b)){
> 	i<-sum(a[which(b==i)])
> }
> 
> i tried to figure out, how tapply works, but neither
> 
> thanks alot
> 
> marc
> --
> 
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