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difference 

        # Array.difference

(from ruby core)
---
    array.difference(*other_arrays) -> new_array

---

Returns a new Array containing only those elements from `self` that are
not found in any of the Arrays `other_arrays`; items are compared using
`eql?`;  order from `self` is preserved:
    [0, 1, 1, 2, 1, 1, 3, 1, 1].difference([1]) # => [0, 2, 3]
    [0, 1, 2, 3].difference([3, 0], [1, 3]) # => [2]
    [0, 1, 2].difference([4]) # => [0, 1, 2]

Returns a copy of `self` if no arguments given.

Related: Array#-.

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