Indicate if elements of a vector are not in another vector.
Examples
x <- c('a', 'v', 'o', 'C', 'a', 'd', 'O')
y <- letters
y %notin% x
#> [1] FALSE TRUE TRUE FALSE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE
#> [13] TRUE TRUE FALSE TRUE TRUE TRUE TRUE TRUE TRUE FALSE TRUE TRUE
#> [25] TRUE TRUE
x %notin% y
#> [1] FALSE FALSE FALSE TRUE FALSE FALSE TRUE