PHP - Sort multi-dimensional array by another array - php

Question

I'm trying to sort a multi-dimensional array by another array, but have so far come up short.
array_multisort seems be working only for real sorting.
Suppose I have these 2 arrays:
$order = array(2,3,1);
$data = array(
array('id' => 1, 'title' => 'whatever'),
array('id' => 2, 'title' => 'whatever'),
array('id' => 3, 'title' => 'whatever')
);
Now I would like to sort my $data array according to the order in my $order array.
This is what I would like the result to be:
$data = array(
array('id' => 2, 'title' => 'whatever'),
array('id' => 3, 'title' => 'whatever')
array('id' => 1, 'title' => 'whatever'),
);
I can accomplish this easily by running a nested loop, but that would not scale well (my array is pretty big, and the arrays have many more fields).

Answer 1

In your example the ids in the $data array are are numbered consecutively and starting at 1. The code I give below assumes this is always the case. If this is not the case, the code does not work.
$result = array();
$index = 0;
foreach ($order as $position) {
$result[$index] = $data[$position - 1];
$index++;
}
At http://codepad.org/YC8w0yHh you can see that it works for your example data.
EDIT
If the assumption mentioned above does not hold, the following code will achieve the same result:
<?php
$data = array(
array('id' => 1, 'title' => 'whatever'),
array('id' => 2, 'title' => 'whatever'),
array('id' => 3, 'title' => 'whatever')
);
$order = array(2,3,1);
$order = array_flip($order);
function cmp($a, $b)
{
global $order;
$posA = $order[$a['id']];
$posB = $order[$b['id']];
if ($posA == $posB) {
return 0;
}
return ($posA < $posB) ? -1 : 1;
}
usort($data, 'cmp');
var_dump($data);
See http://codepad.org/Q7EcTSfs for proof.
By calling array_flip() on the $order array it can be used for position lookup. This is like a hashtable lookup, which is linear in time, or O(n). You cannot do better.

Answer 2

There is no built-in function for this in PHP and i am unable to think of any custom function, which would do this using usort. But array_map is simple enough, imo, so why not use it instead?
$sorted = array_map(function($v) use ($data) {
return $data[$v - 1];
}, $order);

Answer 3

For those of you who want to sort data based on an array with actual IDs, rather than based on an array with indexes like in the accepted answer - you can use the following simple comparison function for the usort:
usort($data, function($a, $b) use ($order) {
$posA = array_search($a['id'], $order);
$posB = array_search($b['id'], $order);
return $posA - $posB;
});
So the following example will work fine and you won't get the Undefined offset notices and an array with null values:
$order = [20, 30, 10];
$data = [
['id' => 10, 'title' => 'Title 1'],
['id' => 20, 'title' => 'Title 2'],
['id' => 30, 'title' => 'Title 3']
];
usort($data, function($a, $b) use ($order) {
$posA = array_search($a['id'], $order);
$posB = array_search($b['id'], $order);
return $posA - $posB;
});
echo '<pre>', var_dump($data), '</pre>';
Output:
array(3) {
[0]=>
array(2) {
["id"]=>
int(20)
["title"]=>
string(7) "Title 2"
}
[1]=>
array(2) {
["id"]=>
int(30)
["title"]=>
string(7) "Title 3"
}
[2]=>
array(2) {
["id"]=>
int(10)
["title"]=>
string(7) "Title 1"
}
}

Answer 4

This would be how I would do. I would use a custom usort function (arr_sort) in conjunction with the $data array.
<?php
$order = array(2,3,1);
$data = array(
array('id' => 1, 'title' => 'whatever'),
array('id' => 2, 'title' => 'whatever'),
array('id' => 3, 'title' => 'whatever')
);
function arr_sort($a,$b){
global $order;
foreach ($order as $key => $value) {
if ($value==$a['id']) {
return 0;
break;
}
if ($value==$b['id']) {
return 1;
break;
}
}
}
usort($data,'arr_sort');
echo "<pre>";
print_r($data);
echo "<pre>";

Answer 5

You could try using a custom sort with usort(). This way you can use the first array to determine the order of the second array.