Sorting an array in order defined by other array

Question

Does PHP have the capability to sort an array of items (A) in an order that is defined by another array (B)? Eg. the item that comes first in B decides which item should come first when sorting A.

$order_to_sort_by = array("Gold", "Silver", "Bronze");
$items_to_sort = array("Bronze", "Silver", "Bronze", "Gold", "Bronze", "Silver");

some_sort_function($items_to_sort, $order_to_sort_by);

Result:

Gold
Silver
Silver
Bronze
Bronze
Bronze

EDIT: The duplicate that was suggested seems to use keys of another array to determine which keys in the array should be used for sorting. Somewhat unclear, but I don't think it's a duplicate.

Possible duplicate of Sort an Array by keys based on another Array? — CodeGodie
– CodeGodie, Commented Feb 8, 2016 at 14:55
I saw that article, but didn't quite grasp what he's doing. It seems like something different. I thought about translating the values in A to the key (index) value of the corresponding item in B, then sort, then translate back. I'll never have more than a few hundred items, so performance is not a critical issue. — forthrin
– forthrin, Commented Feb 8, 2016 at 14:57

Mat · Accepted Answer · 2016-02-08 15:51:17Z

3

You could try something like this

$order_to_sort_by = array("Gold", "Silver", "Bronze");
$items_to_sort = array("Bronze", "Silver", "Bronze", "Gold", "Bronze", "Silver");

$order_to_sort_by_reversed = array_flip($order_to_sort_by);
$sortByArray = function($a, $b) use ($order_to_sort_by_reversed)
{
    return $order_to_sort_by_reversed[$a] - $order_to_sort_by_reversed[$b];
};
usort($items_to_sort, $sortByArray);

var_dump($items_to_sort);

edited Feb 8, 2016 at 15:51

answered Feb 8, 2016 at 14:54

Mat

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4 Comments

forthrin Over a year ago

This is brilliant! Best one so far. Short and simple. Will keep an eye open for even better solutions.

Mat Over a year ago

Does it finally suit your needs?

forthrin Over a year ago

I'm quite happy with this solution for now!

Mat Over a year ago

Great ! I would be glad if you accept the answer, if you think it's ok ;-)

Alex Belyaev · Accepted Answer · 2016-02-08 22:43:33Z

2

You can use usort function to define how to compare elements of array. Example:

$order_to_sort_by = array("Gold", "Silver", "Bronze");
$items_to_sort = array("Bronze", "Silver", "Bronze", "Gold", "Bronze", "Silver");

usort(
    // What to sort. Input array will be changed!
    $items_to_sort, 

    // Lets define comparing function inplace
    // ...just cause we can use anonymous functions: 
    function($a, $b) use ($order_to_sort_by) {
        // Find position of two comparing elements
        // ...in our ranking array to find what element
        // ...is 'greater' than another
        $a_pos = array_search($a, $order_to_sort_by);
        $b_pos = array_search($b, $order_to_sort_by);

        // 0 means that items will not be swapped
        // 1 for moving $b up
        // -1 for moving $b down
        if ($a_pos == $b_pos) {
            return 0;
        } else if ($a_pos > $b_pos) {
            return 1;
        } else {
            return -1;
        }

        // I hope in php7 it would be able
        // to use `spaceship` operator in this case
        // instead of these if`s:
        //     return $a <=> $b
    }
);

var_dump($items_to_sort);

edited Feb 8, 2016 at 22:43

answered Feb 8, 2016 at 15:16

Alex Belyaev

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1 Comment

forthrin Over a year ago

This one makes sense too, but a bit more cumbersome than the $order_to_sort_by_reversed suggestion.

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