[R] descretizing xy data

[Rubén Roa-Ureta]

Jon A wrote:
> Hello,
> I have a dataset with a continuous independent variable (fish length, range:
> 30-150 mm) and a binary response (foraging success, 0 or 1). I want to
> discretize fish length into 5 mm bins and give the proportion of individuals
> who successfully foraged in each each size bin. I have used the cut function
> to discretize the length values into my desired bins, but I can't figure out
> how to manipulate my response data in terms of the levels I've created. Any
> advice on how to achieve my task?
>
> Thanks in advance.
>   
You have the option of using catspec.
Here is another, more transparent solution, using hist().
lb <- 30
ub <- 150
bk <- 5
x <- data.frame(cbind(runif(1000,lb,ub),rbinom(1000,1,0.75)))
x$X3 <- cut(x$X1,breaks=(ub-lb)/bk,labels=FALSE)
y <- 
data.frame(cbind(hist(x$X1,breaks=(ub-lb)/bk,plot=FALSE)$breaks[-1],hist(x$X1,breaks=(ub-lb)/bk,plot=FALSE)$counts,0))
for (i in 1:length(y$X1)) {
  for (j in 1:length(x$X1)) {
     if(identical(x$X3[j],i)) y$X3[i] <- y$X3[i]+x$X2[j]
  }
}
sum(x$X2) #check that counting was correct
sum(y$X3)
y$X4 <- ifelse(y$X3 > 0,y$X3/y$X2,NA)
plot(y$X1,y$X4,pch=19)
abline(v=hist(x$X1,breaks=(ub-lb)/bk,plot=FALSE)$breaks)

HTH
Rubén