Sorting an array by text of first subarray in each row

Question

I have an array stored as $product_categories. A sample of this array is:

$array = [
    [
        ['id' => 10, 'text' => 'Latex'],
        ['id' => 15, 'text' => 'Occasion Latex'],
        ['id' => 82, 'text' => 'Christmas'],
    ],
    [
        ['id' => 11, 'text' => 'Accessories'],
        ['id' => 97, 'text' => 'Retail Accessories'],
        ['id' => 558, 'text' => 'Super Stuffer'],
    ],
    [
        ['id' => 374, 'text' => 'Party Supplies'],
        ['id' => 1488, 'text' => 'Party by Occasion'],
        ['id' => 1493, 'text' => 'Christmas'],
    ],
];

I want to sort it ONLY by the key 'text' in [0], which would give me a result of

[
    [
        ['id' => 11, 'text' => 'Accessories'],
        ['id' => 97, 'text' => 'Retail Accessories'],
        ['id' => 558, 'text' => 'Super Stuffer'],
    ],
    [
        ['id' => 10, 'text' => 'Latex'],
        ['id' => 15, 'text' => 'Occasion Latex'],
        ['id' => 82, 'text' => 'Christmas'],
    ],
    [
        ['id' => 374, 'text' => 'Party Supplies'],
        ['id' => 1488, 'text' => 'Party by Occasion'],
        ['id' => 1493, 'text' => 'Christmas'],
    ],
];

I've tried using

$product_categories = usort($product_categories, 'sortAlphabetically');

function sortAlphabetically($a, $b) {
    return strcmp($a['text'], $b['text']);
}

Using that, a print_r() of the array simply returns 1.

I thought usort() was the correct way to sort the array but clearly I'm doing something wrong here.

usort() sorts the array in place and returns TRUE, it doesn't return the sorted array. — Barmar
– Barmar, Commented Nov 17, 2021 at 0:10
$a['text'] should be $a[0]['text'] if you want to sort by the text in [0], and the same for $b. — Barmar
– Barmar, Commented Nov 17, 2021 at 0:11

mickmackusa · Accepted Answer · 2021-11-17 03:51:21Z

2

You only need to access the subarray data using array syntax as you've expressed in English. (Demo)

usort(
    $array,
    function($a, $b) {
        return $a[0]['text'] <=> $b[0]['text'];
    }
);
var_export($array);

Or in PHP7.4 or higher:

usort($array, fn($a, $b) => $a[0]['text'] <=> $b[0]['text']);

answered Nov 17, 2021 at 3:51

mickmackusa♦

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Comments

cottton · Accepted Answer · 2021-11-17 01:39:59Z

Your array:

$array = [
    '0' => [
        '0' => [
            'id'   => 10,
            'text' => 'Latex',
        ],
        '1' => [
            'id'   => 15,
            'text' => 'Occasion Latex',
        ],
        '2' => [
            'id'   => 82,
            'text' => 'Christmas',
        ],
    ],
    '1' => [
        '0' => [
            'id'   => 11,
            'text' => 'Accessories',
        ],
        '1' => [
            'id'   => 97,
            'text' => 'Retail Accessories',
        ],
        '2' => [
            'id'   => 558,
            'text' => 'Super Stuffer',
        ],
    ],
    '2' => [
        '0' => [
            'id'   => 374,
            'text' => 'Party Supplies',
        ],
        '1' => [
            'id'   => 1488,
            'text' => 'Party by Occasion',
        ],
        '2' => [
            'id'   => 1493,
            'text' => 'Christmas',
        ],
    ],
];

The sort:

// uasort(): "Sort an array with a user-defined comparison function
//            and maintain index association"
uasort($array, function (array $a, array $b) {
    // "I want to sort it ONLY by the key 'text' in [0]"
    // Get first from array (aka [0]).
    // (You could change that to fix $a[0] and $b[0] if you want|need to.)
    $aFirst = reset($a); 
    $bFirst = reset($b); 
    $offset = 'text';
    if ($aFirst[$offset] == $bFirst[$offset]) {
        return 0;
    }
    // a < b === asc ; a > b === desc
    return ($aFirst[$offset] < $bFirst[$offset]) ? -1 : 1;
});
echo var_export($array, true) . PHP_EOL;

Results in:

[
    1 => [
        0 => [
            'id'   => 11,
            'text' => 'Accessories',
        ],
        1 => [
            'id'   => 97,
            'text' => 'Retail Accessories',
        ],
        2 => [
            'id'   => 558,
            'text' => 'Super Stuffer',
        ],
    ],
    0 => [
        0 => [
            'id'   => 10,
            'text' => 'Latex',
        ],
        1 => [
            'id'   => 15,
            'text' => 'Occasion Latex',
        ],
        2 => [
            'id'   => 82,
            'text' => 'Christmas',
        ],
    ],
    2 => [
        0 => [
            'id'   => 374,
            'text' => 'Party Supplies',
        ],
        1 => [
            'id'   => 1488,
            'text' => 'Party by Occasion',
        ],
        2 => [
            'id'   => 1493,
            'text' => 'Christmas',
        ],
    ],
]

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