Grokbase Groups R r-help June 2012
FAQ
HI,

Try this:
dat1 <- read.table(text="
subject??? time.ms V3
1????? 1? stringA
1????? 12? stringB
1????? 22??? stringC
2????? 1??? stringB
2????? 14? stringC
2????? 25? stringA
", sep="",header=TRUE)
dat2<-aggregate(dat1$time.ms,list(dat1$subject),max)
colnames(dat2)<-c("subject","time.ms")


?merge(dat2,dat1)
? subject time.ms????? V3
1?????? 1????? 22 stringC
2?????? 2????? 25 stringA

A.K.




----- Original Message -----
From: Miriam <miriam_katharina@gmx.de>
To: r-help at r-project.org
Cc:
Sent: Tuesday, June 26, 2012 5:21 PM
Subject: [R] selecting rows by maximum value of one variables in dataframe nested by another Variable

How could I select the rows of a dataset that have the maximum value in one variable and to do this nested in another variable. It is a dataframe in long format with repeated measures per subject.?
I was not successful using aggregate, because one of the columns has character values (and/or possibly because of another reason).
I would like to transfer something like this:
subject? ? time.ms? V3
1??? ??? 1??? stringA
1??? ??? 12??? stringB
1??? ??? 22? ??? stringC
2??? ??? 1 ??? stringB
2??? ??? 14??? stringC
2??? ??? 25??? stringA
?.
To something like this:
subject??? ? time.ms??? V3
1??? ??? 22??? stringC
2??? ??? 25 ??? stringA
?

Thank you very much for you help!
Miriam
--

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