Is there an elegant way to do “not in” in Julia?

julia> a = [1, 2, 3, 4, 5];

julia> 6 ∉ a
true

The ∉ symbol can be typed in the REPL by typing \notin and then hitting TAB. Of course, the ∈ symbol is also available as an alternative to in by typing \in and hitting TAB:

julia> 6 ∈ a
false

Sometimes you need a vectorized version:

julia> x = [2, 7];

julia> x .∉ Ref(a)
2-element BitArray{1}:
 0
 1

The Ref is needed in this case so that a is treated as a scalar in the broadcasting operation.

If you prefer to avoid Unicode characters, you can write !(6 in a) instead of 6 ∉ a.