find and sort array by lowest value in multidimensional array

Question

I have an array that contains a number of arrays. Like this:

array{
    array{
        id => 1
        name => place_1
        lat => 56.1705
        lon => 10.2010
        distance => 1.545
    }
    array{
        id => 14
        name => place_14
        lat => 56.1715
        lon => 10.2049
        distance => 1.765
    }
    //etc etc
}

I need to sort the arrays within the array by distance, from low to high - or at least get the position of the lowest distance in the array (like $array[1][4] == 1.765).

I have done something similar before. Then I did it with a function like this:

function sort_by_dist($a, $b){
    return $a['distance'] - $b['distance'];
}
usort($array, 'sort_by_dist');

However, this will in this case only return bool(true) I have no idea why it acts this way.

I know this question has probably been asked (and answered) before, but as a non-native speaker of English I am a bit at a loss as to what I should search for.

Thank you for your help!

By definition, usort will return a boolean as per: php.net/manual/en/function.usort.php the array $array will be sorted according to the function you defined (sort_by_dist) — ymas
– ymas, Commented Nov 27, 2014 at 23:11

ymas · Accepted Answer · 2014-11-27 23:22:20Z

2

My answer just reformats your function a little to make it more explicit what is going on:

$a = array(
    array(
        'id' => 14,
        'name' => 'place_14',
        'lat' => 56.1715,
        'lon' => 10.2049,
        'distance' => 1.765,
    ),
    array(
        'id' => 1,
        'name' => 'place_1',
        'lat' => 56.1705,
        'lon' => 10.2010,
        'distance' => 1.545,
    ),
);

usort($a, function($a, $b) {
    $d1 = $a['distance'];
    $d2 = $b['distance'];

    if ($d1 == $d2) {
        return 0;
    }
    return ($d1 < $d2) ? -1 : 1;
});

// the array $a is sorted.
print_r($a);

The input array to usort is sorted, usort will return false if the sorting failed and true otherwise.

answered Nov 27, 2014 at 23:22

ymas

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felixyadomi · Accepted Answer · 2014-11-27 23:22:24Z

1

You can use array_multisort by iterating thought the array like so:

function sort_by(&$array, $subkey ) {
    foreach ($array as $subarray) {
        $keys[] = $subarray[$subkey];
    }
    array_multisort($keys, SORT_ASC, $array);
}
sort_by($coords, 'distance');// $coords is now sorted by distance

$coords is your multidimensional array.

answered Nov 27, 2014 at 23:22

felixyadomi

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