The challenge

Implement a difference function, which subtracts one list from another and returns the result.

It should remove all values from list a, which are present in list b keeping their order.

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arrayDiff([1,2],[1]) == [2]

If a value is present in b, all of its occurrences must be removed from the other:

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arrayDiff([1,2,2,2,3],[2]) == [1,3]

The solution in Python

Option 1:

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def array_diff(a, b):
    return [x for x in a if x not in b]

Option 2:

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def array_diff(a, b):
    return filter(lambda i: i not in b, a)

Option 3:

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def array_diff(a, b):
    for i in range(len(b)):
        while b[i] in a:
            a.remove(b[i])
    return a

Test cases to validate our solution

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import  test
from solution import array_diff

@test.describe("Fixed Tests")
def fixed_tests():
    @test.it('Basic Test Cases')
    def basic_test_cases():
        test.assert_equals(array_diff([1,2], [1]), [2], "a was [1,2], b was [1], expected [2]")
        test.assert_equals(array_diff([1,2,2], [1]), [2,2], "a was [1,2,2], b was [1], expected [2,2]")
        test.assert_equals(array_diff([1,2,2], [2]), [1], "a was [1,2,2], b was [2], expected [1]")
        test.assert_equals(array_diff([1,2,2], []), [1,2,2], "a was [1,2,2], b was [], expected [1,2,2]")
        test.assert_equals(array_diff([], [1,2]), [], "a was [], b was [1,2], expected []")
        test.assert_equals(array_diff([1,2,3], [1, 2]), [3], "a was [1,2,3], b was [1, 2], expected [3]")