Ruby: Array contained in Array, any order [duplicate]

Question

Suppose I have the following Ruby code:

array_1 = ['a', 'b']
array_2 = ['a', 'b', 'c']

some_function(array_1, array_2) # => True
some_function(array_2, array_1) # => False
some_function(['a', 'b'], ['a', 'd']) # => False
some_function(['x', 'y'], array_2) # => False

I am pretty much looking for some_function to return True when Parameter 2 contains all of the elements in Parameter 1.

Answer 1

def f a,b
    (a-b).empty?
end

Answer 2

From a previous post,

def f a,b
    (a-b).empty?
end

will not work the way you expect, for example:

a1 = [1, 2, 3, 4, 5, 6, 7, 8, 9]
a2 = [2, 3, 5, 9]

(a1-a2).empty? # returns true

however,

a1-a2 # returns [1, 4, 6, 7, 8], not empty

thus f returns false.

A more accurate solution, if you want a one-liner would be:

def f a,b
    a&b == b
end

a&b will return all elements that are in both a and b then we check to see if that is equal to b

For ambiguity sake:

def f a,b
    (a&b == a) || (a&b == b)
end