Output from recursive function R

Question

I'm trying to write a simple recursive function in R which each time will return just a single number. I want to store these in a column basically. So initially I'm declaring something like relevant=c(rep(0,16)) then if it satisfies some criteria I want to change the corresponding values of relevant[j] to 1. if(something==1){ relevant[j]=1 }

But then when I call relevant outside the function all the values are 0. The criteria is definitely being satisfied, but it just doesn't seem to change the values!

Any help would be appreciated!

Answer 1

Here is a "simple enough recursive function" that will return a vector of numbers, each one being calculated inside the function:

serf <- function(x){
            if (length(x)==5) {
              return(x)
            } else {
               x <- c(x, x[length(x)]+1) ; serf(x)
            }
        }


serf(1)
#[1] 1 2 3 4 5

Is that what you had in mind ?

Answer 2

It's not entirely clear to me what you want to do, but I interpret it as having a recursive function that returns a single value and wanting as well to accumulate the results of the recursive calls as a side effect.

Here's an example based on computation of Fibonacci numbers that solves this problem using a closure. A couple of caveats: (1) This is a terribly inefficient way to compute Fibonacci numbers. (2) Building up an object like values element-wise is very inefficient in R; if you know the length of the result in advance, it's much better to initialize the object to that length and then index into it.

> makefib <- function(){
+   values <- vector("numeric")
+   function(n){
+     if (n == 0) return(values)
+     res <- if (n < 3) 1 else Recall(n - 1) + Recall(n - 2)
+     values[length(values) + 1] <<- res
+     res
+   }
+ }   

> fib <- makefib()
> fib(6)
 [1] 8
> fib(0)
 [1] 1 1 2 1 3 1 1 2 5 1 1 2 1 3 8

I hope this helps.