Test set relations among two vectors.
pool(x, y)
The two vectors are tested for elements unique to x, unique to y, and common to both.
If length of x is zero, it is returned unmodified. If length of rule is zero, value is all NA.
pool(letters[1:5], letters[4:8])
#> $x
#> [1] "a" "b" "c"
#>
#> $y
#> [1] "f" "g" "h"
#>
#> $both
#> [1] "d" "e"
#>