[R] sum variable as long condition is true
marcg
mdgi at gmx.ch
Tue Oct 23 13:51:36 CEST 2007
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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