Quick way to check if all items in a Ruby array are unique

Question

I'm looking for a quick and easy way to check if all the items in an array are unique.

unique = ['one', 'two']
unique = []
not_unique = ['one', 'one', 'two']

Answer 1

# As simple as possible:
not_unique == not_unique.uniq

# or perhaps
not_unique.size == not_unique.uniq.size

Answer 2

array & array == array

is another option.