R help - Oct 2008 - Selecting cases for a grouping value to refill x and y vectors

The variable "iter" from read.table takes on values of 0,5,10,15, and
20.  I
am trying to pick off values of iter by assigning it to "grp", and
e.g.
iter<-5, then fill the x and y vectors and make plots of x,y for each value
of iter (>0) 
 
For some reason all of the plots are the same, so I am not changing x and y.
 
Any sugestions on how to refill vectors x and y when iter takes on certain
values?
 
 thx LP
 
> 
> mydata<-read.table("C:/refvecs_iters_5.csv", header=TRUE,
sep=",",
na.strings="NA", dec=".", strip.white=TRUE,
row.names=1)
> 
> x <- runif(1000)
> y <- runif(1000)
> 
> summary(mydata)
      iter         xin                yin          
 Min.   : 0   Min.   : 0.01792   Min.   : 0.03055  
 1st Qu.: 5   1st Qu.: 3.10674   1st Qu.: 3.13284  
 Median :10   Median : 5.46899   Median : 5.43446  
 Mean   :10   Mean   : 5.43360   Mean   : 5.39696  
 3rd Qu.:15   3rd Qu.: 7.70127   3rd Qu.: 7.70780  
 Max.   :20   Max.   :10.00000   Max.   :10.00000  
> 
> #plot(mydata$xin,mydata$yin)
> 
> split.screen(c(2,2))
[1] 1 2 3 4
> 
> for (k in 1:4){
+ 
+   screen(k)  
+   cnt <- 0
+   grp<- mydata$iter * 5
+   for (i in 1:5000 ) {
+     if (grp<-k*5) {
+      cnt = cnt + 1
+      x[cnt] <- mydata$xin[i]
+      y[cnt] <- mydata$yin[i]
+     }
+   }
+   #p = cbind(x=rnorm(300), y=rnorm(300))
+   #p = cbind(x, y)
+   #tt = delaunayn(p)
+   #trimesh(tt,p,axis=TRUE,box=TRUE)
+   plot(x,y)
+ }
> 
> 

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