Union, Difference and Intersect with Ruby Arrays

Union

> [:a, :b, :c].union([:b, :c, :d])
 => [:a, :b, :c, :d]

Difference

> [:a, :b, :c].difference([:b, :c, :d])
 => [:a]

Intersect

> [:a, :b, :c] & [:b, :c, :d]
 => [:b, :c]