Identifying elements of a vector which is not found in another comparable vector in R

Question

I want to know the exact elements of a vector not found in the vector. For instance, consider the following vectors:

veca <- c("ab", "cd", "ef", "gh", "ij", "kl")
vecb <- c("ab", "ef", "ij", "kl")

From this, cd and gh are in veca but not in vecb. How can one identify these elements in R? Thanks!

Does this answer your question? [Compare two character vectors in R](https://stackoverflow.com/questions/17598134/compare-two-character-vectors-in-r) — S-SHAAF, Apr 17 '23 at 21:10

score 3 · Accepted Answer · answered Apr 17 '23 at 20:17

We could define a custom function like an opposite intersect function using setdiff:

learned here:

outersect <- function(x, y) {
  sort(c(setdiff(x, y),
         setdiff(y, x)))
}

outersect(veca, vecb)

output:

[1] "cd" "gh"

Another possible solution is:

not_in_vecb <- veca[!veca %in% vecb]

[1] "cd" "gh"

score 2 · Answer 2 · answered Apr 17 '23 at 20:34

2

You can use %in% operator

Identifying elements in veca that are not in vecb

> veca[!(veca %in% vecb)]
[1] "cd" "gh"

answered Apr 17 '23 at 20:34

Popppin.piet

score 2 · Answer 3 · answered Apr 17 '23 at 20:49

Here we consider a bit more general case

veca <- c("ab", "cd", "ef", "gh", "ij", "kl") # "cd" and "gh" are not in `vecb`
vecb <- c("ab", "ef", "ij", "kl", "xy") # "xy" is not in `veca`

Below are some options we can try

> setdiff(union(veca, vecb), intersect(veca, vecb))
[1] "cd" "gh" "xy"

subset(
  aggregate(
    ind ~ .,
    stack(list(a = veca, b = vecb)),
    unique
  ),
  lengths(ind) == 1,
  select = values
)

which gives

  values
2     cd
4     gh
7     xy

score 1 · Answer 4 · answered Apr 17 '23 at 20:16

1

You can use the builtin function setdiff()

Example:

veca <- c("ab", "cd", "ef", "gh", "ij", "kl")
vecb <- c("ab", "ef", "ij", "kl")


print(setdiff(veca, vecb))

Output:

[1] "cd" "gh"

answered Apr 17 '23 at 20:16

stressed

4 Answers4