Sort array values by their existence in a blacklist array, then alphabetically

Question

I have the following code:

$check = array('person a','person c');
$data = array('person c','person a','person d','person e');
define('check',$check);
//asort($data);

print'<pre>';print_r($data);print'</pre>';

usort($data,function($a,$b){
    return empty(check[$a]) ? 1 : $a <=> $b;
});

print'<pre>';print_r($data);print'</pre>';
exit;

What I am trying to achieve is:

person d
person e
person a
person c

What I get is

person e
person a
person d
person c

Because person a and c are in the $check array, I'm trying to sort my array based on alphabetically for those not in the $check group and then those who are. I could probably split things up a bit and am not overly familiar with the usort custom functions, but is it possible to acheive it this way?

Answer 1

Create a "mapping" array using array_map() and in_array() to flag each $data item, then array_multisort() both the mapping array and the $data array:

<?php

$check = array('person a','person c');
$data = array('person c','person a','person d','person e');

function dmap ($itm) {
    GLOBAL $check;
    return ((int)in_array($itm, $check)+1) . $itm;
}

$mm = array_map('dmap', $data);
array_multisort($mm, $data);
print_r($data);

exit;

Outputs:

Array
(
    [0] => person d
    [1] => person e
    [2] => person a
    [3] => person c
)

When providing two arrays to array_multisort() the function sorts the first array, ascending by default, and applies the sorted order of the first array to the second.

The "mapping" array simply prepends a 1 or 2 to each element of the $data array to affect the sort order moving the items not found in the $check into first sort position.

Try it here: https://onlinephp.io/c/5ae10