Word counter:
Array
(
    [hello] => 3
    [world] => 1
)
Matrix 3x3:
Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 1
            [2] => 1
        )

    [1] => Array
        (
            [0] => 1
            [1] => 1
            [2] => 1
        )

    [2] => Array
        (
            [0] => 1
            [1] => 1
            [2] => 1
        )

)
Set:
Array
(
    [0] => 1
    [1] => 2
    [2] => hello
    [3] => world
    [4] => 3
    [5] => 4
    [6] => answer
    [7] => 42
)
Set:
Array
(
    [0] => 1
    [1] => 2
    [2] => world
)
Intersection:
Array
(
    [0] => 1
    [1] => 2
)
Difference:
Array
(
    [0] => world
)
Union:
Array
(
    [0] => 1
    [1] => 2
    [2] => world
    [3] => 3
)