How do I compare two arrays filled with hashes and return the hashes that are not present in the second?

Question

Let's say I have two arrays filled with hashes,

array_a = [{'key' => 'a'}, {'key' => 'b'}, {'key' => 'c'}, {'key' => 'd'}]
array_b = [{'key' => 'a'}, {'key' => 'b'}, {'key' => 'd'}]

how do I compare array_a and array_b and return the hash that was not found in array_b .

So the compare should return:

# => [{'key' => 'c'}]

Answer 1

Array#- would work:

array_a = [{'key' => 'a'}, {'key' => 'b'}, {'key' => 'c'}, {'key' => 'd'}]
array_b = [{'key' => 'a'}, {'key' => 'b'}, {'key' => 'd'}]

array_a - array_b
#=> [{"key"=>"c"}]

The method "… compares elements using their hash and eql? methods …" and according to Hash#hash :

Two hashes with the same content will have the same hash code (and will compare using eql? ).