Returning absent values without inducing integer (0)

Question

I want to identify which values in one vector are present in another vector. Sometimes, in my application, none of the values of the first vector are present; in such cases I would like NA. My current approach returns integer(0) when this occurs:

l <- 1:3
m <- 2:5
n <- 4:6
l[l %in% m]

1] 2 3

l[l %in% n]

integer(0)

This post discusses how to capture integer(0) using length, but is there a way to avoid integer(0) in the first place, and do this operation in just one step? Answers to the previous question suggest that any could be used but I fail to see how that would work in this example.

`i <- l %in% n; if (any(i)) l[i] else NA` – jogo Jun 14 '19 at 11:57 — jogo, Jun 14 '19 at 11:57

score 2 · Accepted Answer · answered Jun 14 '19 at 11:57

You could catch the integer(0) with a custom function:

l <- 1:3
m <- 2:5
n <- 4:6

returnsafe <- function(a, b) {
    result <- a[a %in% b]
    if(is.integer(result) && length(result) == 0L) {
        return(NA)
    } else {
        return(result)
    }
}


> returnsafe(l, n)
[1] NA

score 1 · Answer 2 · answered Jun 14 '19 at 11:55

1

You can do:

l[match(l, n)]

[1] NA NA NA

Or:

any(l[match(l, n)])

[1] NA

answered Jun 14 '19 at 11:55

tmfmnk

38,881
4
47
67

Returning absent values without inducing integer (0)

2 Answers2