[R] Need help for loop code, thanks

[Phil Spector]

Is this what you're looking for?

> 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)
> aggregate(dat$v3,dat[c('V1','V2')],max)
   V1 V2   x
1  1  a 7.0
2  2  a 5.3
3  1  b 2.0
4  1  c 5.5
5  2  c 5.0
6  1  d 6.0
7  2  f 4.0
8  2  g 4.6

 					- Phil Spector
 					 Statistical Computing Facility
 					 Department of Statistics
 					 UC Berkeley
 					 spector at stat.berkeley.edu



On Thu, 7 Oct 2010, wangguojie2006 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,
>
>
>
>
>
> -- 
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>
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