[R] Need help for loop code, thanks

[wangguojie2006]

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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