Recursive function sum of digits R

Question

I try to write a recursive function that returns the sum of digits. However, the program below doesn't seem to do the trick.

getSum = function(i) {
    if (i < 0) {Print("Please enter a positive number")}
    if (i >= 0) {getSum(i - floor(i / 10) - i %% 10) + floor(i / 10) + i %% 10}

It gives two errors:

Error: evaluation nested too deeply: infinite recursion / options(expressions=)?
Error during wrapup: evaluation nested too deeply: infinite recursion / 
options(expressions=)?

What can I do to solve this?

Answer 1

Use this

if (i >= 0)
{sum(sapply(strsplit(as.character(i),""),as.numeric))}

Of course this works for whole numbers. If your need is greater more regex can be added to accommodate that

Edited! Oops totally missed that you want a recursive function

Answer 2

Do you want something like this?

getSum = function(i){
    i = abs(floor(i))
    if (nchar(i) == 1){
        return(i)
    } else {
        getSum(floor(i/10)) +i%%10 #Minorpt (suggested by @DashingQuark)
    }
}

Answer 3

In R, it is recommended to use Recall for creating a recursive function.

I am using @db's function, but demonstrating with Recall

getSum = function( i ) 
{
  if (nchar(i) == 1){
    return(i)
  } else if (i < 0 ) {
    "Please enter a positive number"
  }else {
    print(i)
    Recall( i = floor(i/10)) +i%%10 
  }
}

getSum(0)
# [1] 0
getSum(1)
# [1] 1
getSum(-1)
# [1] "Please enter a positive number"
getSum(5)
# [1] 5
getSum(100)
# [1] 100
# [1] 10
# [1] 1
getSum( 23)
# [1] 23
# [1] 5