select rows with largest value of variable within a group in r
Posted
by Misha
on Stack Overflow
See other posts from Stack Overflow
or by Misha
Published on 2010-05-12T19:35:01Z
Indexed on
2010/05/12
22:24 UTC
Read the original article
Hit count: 220
Filed under:
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?
© Stack Overflow or respective owner
