Sort multidimensional array by multiple keys

Question

I\'m trying to sort a multidimensional array by multiple keys, and I have no idea where to start. I looked at uasort, but wasn\'t quite sure how to write a function for what

Answer 1

You can do it with usort. The $cmp_function argument could be:

function my_sorter($a, $b) {
    $c = strcmp($a['state'], $b['state']);
    if($c != 0) {
        return $c;
    }

    $c = strcmp($a['event_type'], $b['event_type']);
    if($c != 0) {
        return $c;
    }

    return strcmp($a['date_start'], $b['date_start']);
}

For an arbitrary number of fields in PHP 5.3, you can use closures to create a comparison function:

function make_cmp($fields, $fieldcmp='strcmp') {
    return function ($a, $b) use (&$fields) {
        foreach ($fields as $field) {
            $diff = $fieldcmp($a[$field], $b[$field]);
            if($diff != 0) {
                return $diff;
            }
        }
        return 0;
    }
}

usort($arr, make_cmp(array('state', 'event_type', 'date_start')))

For an arbitrary number of fields of different types in PHP 5.3:

function make_cmp($fields, $dfltcmp='strcmp') {
    # assign array in case $fields has no elements
    $fieldcmps = array();
    # assign a comparison function to fields that aren't given one
    foreach ($fields as $field => $cmp) {
        if (is_int($field) && ! is_callable($cmp)) {
            $field = $cmp;
            $cmp = $dfltcmp;
        }
        $fieldcmps[$field] = $cmp;
    }
    return function ($a, $b) use (&$fieldcmps) {
        foreach ($fieldcmps as $field => $cmp) {
            $diff = call_user_func($cmp, $a[$field], $b[$field]);
            if($diff != 0) {
                return $diff;
            }
        }
        return 0;
    }
}

function numcmp($a, $b) {
    return $a - $b;
}
function datecmp($a, $b) {
    return strtotime($a) - strtotime($b);
}
/**
 * Higher priority come first; a priority of 2 comes before 1.
 */
function make_evt_prio_cmp($priorities, $default_priority) {
    return function($a, $b) use (&$priorities) {
        if (isset($priorities[$a])) {
            $prio_a = $priorities[$a];
        } else {
            $prio_a = $default_priority;
        }
        if (isset($priorities[$b])) {
            $prio_b = $priorities[$b];
        } else {
            $prio_b = $default_priority;
        }
        return $prio_b - $prio_a;
    };
}

$event_priority_cmp = make_evt_prio_cmp(
    array('meeting' => 5, 'party' => 10, 'concert' => 7), 
    0);

usort($arr, make_cmp(array('state', 'event' => $event_priority_cmp, 'date_start' => 'datecmp', 'id' => 'numcmp')))