PHP: Finding distinct values from multidimensional associative array

Question

I have an array not too different from the below (with a lot more sub-arrays). There are any number of sub-arrays and any level of arrays below them. It's only ever this many levels deep however.

Let's say I wanted to bring back all unique pets (in [1]) how would go about doing that? Similarly, if I wanted all unique colours (in [2]) or all unique cars [in [3]]

I tried solutions from How to remove duplicate values from a multi-dimensional array in PHP and other similar SO pages but got nowhere fast and now back to a blank page

Any advice?

Array
(
    [0] => Array
        (
            [0] => Array
                (
                    [0] => Jo Bloggs
                    [1] => Cat
                    [2] => Red
                    [3] => Nissan
                )
            [1] => Array
                (
                    [0] => Patrick
                    [1] => Dog
                    [2] => Blue
                    [3] => Nissan
                )
        )
    [1] => Array
        (
            [0] => Array
                (
                    [0] => Charloe
                    [1] => Moose
                    [2] => Green
                    [3] => Ford
                )
            [1] => Array
                (
                    [0] => Patrick
                    [1] => Dog
                    [2] => Blue
                    [3] => Porsche
                )
        )
...

Answer 1

PHP offers a wide range of convenience functions to handle array. I strongly suggest that you dive into the official documentation and start getting creative yourself: http://php.net/manual/en/ref.array.php

Here is a simple example of the actual algorithm you asked using two such functions:

<?php  
$input = [
    [
        [
            0 => "Jo Bloggs",
            1 => "Cat",
            2 => "Red",
            3 => "Nissan"
        ],
        [
            0 => "Patrick",
            1 => "Dog",
            2 => "Blue",
            3 => "Nissan"
        ],
    ],
    [
        [
            0 => "Charloe",
            1 => "Moose",
            2 => "Green",
            3 => "Ford"
        ],
        [
            0 => "Patrick",
            1 => "Dog",
            2 => "Blue",
            3 => "Porsche"
        ]
    ]
];

$aspect = 1;
$output = [];
array_walk_recursive($input, function($value, $key) use ($aspect, &$output) {
    if ($key == $aspect) {
        $output[] = $value;
    }
});

print_r(array_unique($output));

The output of above code obviously is:

Array
(
    [0] => Cat
    [1] => Dog
    [2] => Moose
)

What type of elements are filtered out can be controlled via the $aspect variable, it holds the keys you want to identify matches with.

Obviously there are other approaches to what you asked, this is just a simple example. One might also prefer to accept only unique values in the $output array, for example, that would save the final call to array_unique()...