select rows with largest value of variable within a group in r
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by Misha
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Published on 2010-05-12T19:35:01Z
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2010/05/12
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groupwise-maximum
|r
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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