You could use Ruby's Set class:
>> require 'set' #=> true
>> a = [*1..5] #=> [1, 2, 3, 4, 5]
>> b = [*1..3] #=> [1, 2, 3]
>> a.to_set.superset? b.to_set #=> true
For small arrays I usually do the same as what fl00r suggested:
>> (b-a).empty? #=> true
