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?

can you accept the best answer? – eduardokapp May 14 '21 at 13:45 — eduardokapp, May 14 '21 at 13:45

eduardokapp · Answer 1 · 2023-04-17T21:04:51.730

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

score 2 · Answer 2 · answered Apr 09 '21 at 19:31

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

answered Apr 09 '21 at 19:31

ThomasIsCoding

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Suggestion: using `if / else` as you did is not useful. There are only two possible outcomes, so you could just: `if (!length(res)) return(NULL)` and right after it `return(res)` – eduardokapp Apr 09 '21 at 19:38
@eduardokapp yes, exactly, we can do it like that. – ThomasIsCoding Apr 09 '21 at 19:42

score 1 · Answer 3 · answered Jun 27 '21 at 00:39

This works regardless of the order of arguments. First this function sorts the arguments, then determines the minimum and maximum values in the sequence (exclusive of integer boundaries), then returns the sequence as requested.

integers_in_between<-function(x,y){
        values<-sort(c(x,y))
        minimum<-ifelse(ceiling(values[1])==values[1], ceiling(values[1])+1, ceiling(values[1]))
        maximum<-ifelse(floor(values[2])==values[2], floor(values[2])-1, floor(values[2]))
        if(maximum-minimum<0){
                NULL
        }else{
                minimum:maximum
        }
}

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

3 Answers3