you can use sqldf:
> dat = read.table(textConnection('V1 V2 v3
+
+ 1 a 1.3
+ 1 a 1.5
+ 1 b 2.0
+ 1 a 2.3
+ 1 a 3.4
+ 1 c 5.5
+ 1 d 6.0
+ 1 a 7.0
+ 2 f 1.5
+ 2 g 1.6
+ 2 f 3.4
+ 2 f 4.0
+ 2 g 4.6
+ 2 c 5.0
+
+ 2 a 5.3'),header=TRUE)
> closeAllConnections()
> require(sqldf)
> sqldf("select V1, V2, max(V3) from dat group by V1, V2")
V1 V2 max(V3)
1 1 a 7.0
2 1 b 2.0
3 1 c 5.5
4 1 d 6.0
5 2 a 5.3
6 2 c 5.0
7 2 f 4.0
8 2 g 4.6
>
On Thu, Oct 7, 2010 at 11:39 AM, wangguojie2006
<wangguojie2...@gmail.com> wrote:
>
> Dear fellows,
>
> I've been working this problem for a day and still can't see where the
> problem is. I really appreciate if anyone can help me out.
>
> My data is like:
>
> V1 V2 v3
> 1 a 1.3
> 1 a 1.5
> 1 b 2.0
> 1 a 2.3
> 1 a 3.4
> 1 c 5.5
> 1 d 6.0
> 1 a 7.0
> 2 f 1.5
> 2 g 1.6
> 2 f 3.4
> 2 f 4.0
> 2 g 4.6
> 2 c 5.0
> 2 a 5.3
>
> What I want to do is to get the max value of V3 for each unique V2 in each
> V1. For example, when V1=1, unique V2 is (a, b, c, d), and corresponding max
> value of V3 is (7.0, 2.0, 5.5, 6.0). And V1=2, unique V2 is (f, g, c, a) and
> max value of V3 is (4.0, 4.6, 5.0, 5.3). Then combinne these max values.
>
> My code is like:
>
> z<-NULL
> x<-NULL;y<-NULL
> for (j in 1:2)
> {
> x<-unique(V2[V1==j])
> for (i in 1:length(x))
> {
> y[i]<-max(V3[V2==x[i] & V1==j])
> }
> z<-c(z,y)
> }
> length(z)
>
> My problem is the length of z is much bigger than the length of I'm supposed
> to get, like above data, I should only get 8 max values. But the code will
> return me a number bigger than 8. I'm thinking there might be some
> overlapping problem. Can someone help?
>
> Thank you for your time.
>
> Best,
>
>
>
>
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/Need-help-for-loop-code-thanks-tp2967036p2967036.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
--
Jim Holtman
Cincinnati, OH
+1 513 646 9390
What is the problem that you are trying to solve?
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