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Alex Rivera
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a.2<-sample(1:10,100,replace=T) b.2<-sample(1:100,100,replace=T) a.3<-data.frame(a.2,b.2) r<-sapply(split(a.3,a.2),function(x) which.max(x$b.2)) a.3[r,] returns the list index, not the index for the entire data.frame Im trying to return the largest value of b.2 for each subgroup of a.2 . How can I do this efficiently?
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