PHP sort array by priority

Question

I need a method that sorts an array of items by priority.

Here is what I have working so far:

function arraySortPriority(array &$array, $offset, array $priorities)
{
    uasort($array, function ($a, $b) use ($offset, $priorities) {
        if (!isset($a[$offset])) {
            $a[$offset] = null;
        }
        if (!isset($b[$offset])) {
            $b[$offset] = null;
        }
        if ($a[$offset] == $b[$offset]) {
            return 0;
        }
        $aPriority = isset($priorities[$a[$offset]])
            ? $priorities[$a[$offset]]
            : null;
        $bPriority = isset($priorities[$b[$offset]])
            ? $priorities[$b[$offset]]
            : null;
        return $aPriority > $bPriority ? -1 : 1;
    });
}

// an array to sort
$array = [
    ['type' => 'A'],
    ['type' => 'A'],
    ['type' => 'B'],
    ['type' => 'B'],
    ['type' => 'C'],
    ['type' => 'C'],
    ['type' => 'D'],
    ['type' => 'D'],
    ['type' => 'E'],
    ['type' => 'E'],
    ['type' => 'F'],
    ['type' => 'F'],
    ['type' => 'G'],
    ['type' => 'G'],
    ['type' => 'H'],
    ['type' => 'H'],
    ['type' => 'Foo'],
    ['type' => 'Foo'],
    ['type' => 'Bar'],
    ['type' => 'Bar'],
    [0 => 'no type should be last'],
    [0 => 'no type should be last'],
];
// shuffle the array
shuffle($array);
// set priorities
$priorities = [
    'A' => 8,
    'B' => 7,
    'C' => 6,
    'D' => 5,
    'E' => 4,
    'F' => 3,
    'G' => 2,
    'H' => 1,
];
// call
arraySortPriority($array, 'type', $priorities);
// test output
foreach ($array as $item) {
    if (isset($item['type'])) {
        echo "{$item['type']}\r\n";
    } else {
        $values = array_values($item);
        echo reset($values) . PHP_EOL;
    }
}

Expected:

A
A
B
B
C
C
D
D
E
E
F
F
G
G
H
H
Foo
Foo
Bar
Bar
no type should be last
no type should be last

Actual:

A
A
B
B
C
C
D
D
E
E
F
F
G
G
H
H
no type should be last   <-- should be at bottom
no type should be last   <-- should be at bottom
Bar
Bar
Foo
Foo

The problem is that the items that have not been given an $offset should be always sorted to the bottom.

This means that no type should be last should always be sorted lower than Foo or Bar.

How can I do this?

score 2 · Answer 1 · answered May 24 '18 at 14:11

<?php 

// an array to sort
$array = [
    ['type' => 'A'],
    ['type' => 'A'],
    ['type' => 'B'],
    ['type' => 'B'],
    ['type' => 'C'],
    ['type' => 'C'],
    ['type' => 'D'],
    ['type' => 'D'],
    ['type' => 'E'],
    ['type' => 'E'],
    ['type' => 'F'],
    ['type' => 'F'],
    ['type' => 'G'],
    ['type' => 'G'],
    ['type' => 'H'],
    ['type' => 'H'],
    ['type' => 'Foo'],
    ['type' => 'Foo'],
    ['type' => 'Bar'],
    ['type' => 'Bar'],
    [0 => 'no type should be last'],
    [0 => 'no type should be last'],
];
// shuffle the array
shuffle($array);
// set priorities
$priorities = [
    'A' => 8,
    'B' => 7,
    'C' => 6,
    'D' => 5,
    'E' => 4,
    'F' => 3,
    'G' => 2,
    'H' => 1,
];

uasort($array,function($a,$b) use ($priorities){
        if(!isset($a['type'])){
            if(!isset($b['type'])) return -1;
            return 1;
        }else if(!isset($b['type'])){
            return -1;
        }

        if(isset($priorities[$a['type']])){
            if(!isset($priorities[$b['type']])) return -1;

            if($priorities[$a['type']] > $priorities[$b['type']]) return -1;
            else if($priorities[$a['type']] < $priorities[$b['type']]) return 1;

        }else if(isset($priorities[$b['type']])){
            return 1;           
        }

        return 0;
});

echo "<pre>";
print_r($array);

OUTPUT

Array
(
    [21] => Array
        (
            [type] => A
        )

    [8] => Array
        (
            [type] => A
        )

    [18] => Array
        (
            [type] => B
        )

    [20] => Array
        (
            [type] => B
        )

    [6] => Array
        (
            [type] => C
        )

    [16] => Array
        (
            [type] => C
        )

    [11] => Array
        (
            [type] => D
        )

    [1] => Array
        (
            [type] => D
        )

    [7] => Array
        (
            [type] => E
        )

    [17] => Array
        (
            [type] => E
        )

    [13] => Array
        (
            [type] => F
        )

    [5] => Array
        (
            [type] => F
        )

    [15] => Array
        (
            [type] => G
        )

    [9] => Array
        (
            [type] => G
        )

    [4] => Array
        (
            [type] => H
        )

    [0] => Array
        (
            [type] => H
        )

    [19] => Array
        (
            [type] => Bar
        )

    [10] => Array
        (
            [type] => Foo
        )

    [14] => Array
        (
            [type] => Bar
        )

    [12] => Array
        (
            [type] => Foo
        )

    [2] => Array
        (
            [0] => no type should be last
        )

    [3] => Array
        (
            [0] => no type should be last
        )

)

I decided to use your edited solution. See https://stackoverflow.com/a/50513717/3411766. — cottton, May 24 '18 at 16:05

score 2 · Answer 2 · answered Sep 08 '20 at 11:57

You have 3 logical rules for your sorting. The spaceship operators affords a very clear and concise syntax without the mess of condition blocks.

Just write corresponding elements on both sides of the 3-way comparison operator (<=>) and the rules will be honored from left to right. When $b is the first/top/left array, then DESC order is applied; conversely, $a in the first/top/left array equates to ASC sorting.

sort by the existence of the targeted column DESC
then to break #1 ties, sort by the priority value DESC
then to break #2 ties, sort by the target column value ASC

Code: (Demo)

function arraySortPriority(array &$array, $column, array $priorities):void
{
    usort($array, function($a, $b) use ($column, $priorities) {
        $aFocus = $a[$column] ?? null;
        $bFocus = $b[$column] ?? null;
        return [array_key_exists($column, $b), $priorities[$bFocus] ?? 0, $aFocus]
               <=>
               [array_key_exists($column, $a), $priorities[$aFocus] ?? 0, $bFocus];
    });
}

arraySortPriority($array, 'type', $priorities);
var_export($array)

_{If your $array will never contain null values, then this snippet can be further refined to contain no function calls inside of the usort() scope.}

score 1 · Accepted Answer · answered May 24 '18 at 16:03

I decided to use @vivek_23 (edited|fixed) solution.

I edited out unnecessary else and changed the return value to zero if f.e. both offsets not set.

If a and b are missing the offset or have no priority the function should return zero imo.

Working code:

uasort($array, function ($a, $b) use ($offset, $priorities) {
    if (!isset($a[$offset])) {
        return !isset($b[$offset])
            ? 0
            : 1; // down
    } elseif (!isset($b[$offset])) {
        return -1; // up
    }
    if (isset($priorities[$a[$offset]])) {
        if (!isset($priorities[$b[$offset]])) {
            return -1; // up
        }
        return $priorities[$a[$offset]] > $priorities[$b[$offset]]
            ? -1 // up
            : 1; // down
    }
    return isset($priorities[$b[$offset]])
        ? 1 // down
        : 0;
});

This allows me to use negative priority, float priority and i do not override priorities (see -99999999 @Eddie solution).

Tested

// expect A, A, B, B, C, C, ... "no type ..." at bottom
$priorities = [
    'A' => 8,
    'B' => 7,
    'C' => 6,
    'D' => 5,
    'E' => 4,
    'F' => 3,
    'G' => 2,
    'H' => 1,
];

// expect "no type ..." at bottom, ..., C, C, B, B, A, A
$priorities = [
    'A' => -8,
    'B' => -7,
    'C' => -6,
    'D' => -5,
    'E' => -4,
    'F' => -3,
    'G' => -2,
    'H' => -1,
];

// expect B, B, A, A, C, C, ... "no type ..." at bottom
$priorities = [
    'A' => 6.5,
    'B' => 7,
    'C' => 6,
    'D' => 5,
    'E' => 4,
    'F' => 3,
    'G' => 2,
    'H' => 1,
];

// expect "no type ..." at bottom, ..., C, C, A, A, B, B
$priorities = [
    'A' => -6.5,
    'B' => -7,
    'C' => -6,
    'D' => -5,
    'E' => -4,
    'F' => -3,
    'G' => -2,
    'H' => -1,
];

Thanks @vivek_23 :)

score 0 · Answer 4 · answered May 24 '18 at 14:06

You are not handling the case where both priorities are the same.

Solution 1

Simply add the following to your function before the ternary:

if ($aPriority == $bPriority)
    return 0;

So it should look like this:

uasort($array, function ($a, $b) use ($offset, $priorities) {
    if (!isset($a[$offset])) {
        $a[$offset] = null;
    }
    if (!isset($b[$offset])) {
        $b[$offset] = null;
    }
    if ($a[$offset] == $b[$offset]) {
        return 0;
    }

    $aPriority = isset($priorities[$a[$offset]])
        ? $priorities[$a[$offset]]
        : null;
    $bPriority = isset($priorities[$b[$offset]])
        ? $priorities[$b[$offset]]
        : null;

    if ($aPriority == $bPriority)
        return 0;

    return $aPriority > $bPriority ? -1 : 1;
});

Otherwise, you simply assume that $aPriority is less than $bPriority if it's not greater but it can be equal.

Solution 2

Another way to achieve it without an extra if case is to set the priority to 0 instead of null if it's not set:

$aPriority = isset($priorities[$a[$offset]])
    ? $priorities[$a[$offset]]
    : 0;
$bPriority = isset($priorities[$b[$offset]])
    ? $priorities[$b[$offset]]
    : 0;

Then return the subtraction:

return $bPriority - $aPriority;

So it would look like this:

uasort($array, function ($a, $b) use ($offset, $priorities) {
    if (!isset($a[$offset])) {
        $a[$offset] = null;
    }
    if (!isset($b[$offset])) {
        $b[$offset] = null;
    }
    if ($a[$offset] == $b[$offset]) {
        return 0;
    }

    $aPriority = isset($priorities[$a[$offset]])
        ? $priorities[$a[$offset]]
        : 0;
    $bPriority = isset($priorities[$b[$offset]])
        ? $priorities[$b[$offset]]
        : 0;

    return $bPriority - $aPriority;
});

PHP sort array by priority

4 Answers4

Solution 1

Solution 2

Linked