how to access global/outer scope variable from R apply function?

Question

I can\'t seem to make apply function access/modify a variable that is declared outside... what gives?

    x = data.frame(age=c(11,12,13), weight=c(100,105,11         


        

Answer 1

try the following inside your apply. Experiment with the value of n. I believe that for i it should be one less than for z.

         assign("i", i+1, envir=parent.frame(n=2))
         assign("z", z+1, envir=parent.frame(n=3))

---

testme <- function(df) {
    i <- 0
    apply(df, 1, function(x) {
        age <- x[1]
        weight <- x[2]
        cat(sprintf("age=%d, weight=%d\n", age, weight))

        ## ADDED THESE LINES
         assign("i", i+1, envir=parent.frame(2))
         assign("z", z+1, envir=parent.frame(3))

    })
    cat(sprintf("i=%d\n", i))
    i
}

OUTPUT

> z <- 0
> y <- testme(x)
age=11, weight=100
age=12, weight=105
age=13, weight=110
i=3
> cat(sprintf("y=%d, z=%d\n", y, z))
y=3, z=3