How to find out all integers between two real numbers using R

Question

Problem: how can I write a function that receives a and b as inputs and returns all integers inbetween them. So, assuming we have a function called integers_inbetween that behaves like this, we should expect the following examples:

# Returns an array of integers in between a and b
integers_inbetween(1, 4)
[1] 2 3

and

# Returns an array of integers in between a and b
integers_inbetween(4, 1)
[1] 2 3

And

# Returns NULL if there are no integers inbetween a and b
integers_inbetween(3.5, 4)
[1] NULL

How can one implement that logic in R?

Answer 1

This solution should work. I'm assuming the function should work if a > b and also if not. The way I wrote it, if after rounded a == b, the function returns NULL.

inbetween_integers <- function(a, b) {
    a <- round(a)
    b <- round(b)
    if (abs(a - b) <= 1)
        return(NULL)
    if (b < a)
        return(seq.int(from = b + 1, length.out = abs(a - b) - 1))
    return(seq.int(from = a + 1, length.out = abs(a - b) - 1))
}

Answer 2

You can try the code below

inbetween_integers <- function(a, b) {
  u <- sort(c(a, b))
  res <- setdiff(ceiling(u[1]):floor(u[2]), c(a, b))
  if (!length(res)) {
    NULL
  } else {
    res
  }
}

and you will see

> inbetween_integers(1, 4)
[1] 2 3

> inbetween_integers(4, 1)
[1] 2 3

> inbetween_integers(3.5, 4)
NULL