Sorting two associative arrays based on different keys - php

Question

I have the following two associative arrays:
$arr1 = array(
'id' => 1,
'text' => 'Some text is here',
'timestamp' => 130458750
)
$arr2 = array(
'post_id' => 12,
'content' => 'Some content is here too',
'created_at' => 1402154823
)
I want to sort these two arrays based on timestamp and created_at keys, i.e. the larger integer is first and lesser second and so on. Is that possible using PHP's built-in functions? If not, how may I approach the problem?
EDIT
The desired result is: Here, $arr1's timestamp is less and $arr2's timestamp (i.e. created_at) is larger. So, I want to get a combination of $arr1 and $arr2 where $arr2 is first and $arr1 is second. Something like:
$sorted_arr = array($arr2, $arr1);

Answer 1

First let me say that one of your array contains timestamp and second contains created_at. I assumed both of them should be created_at.
In case you want to "sort" just two entries like you said in the comments, the task is straightforward:
<?php
$arr1 = array(
'id' => 1,
'text' => 'Some text is here',
'created_at' => 130458750 #corrected from "timestamp"
);
$arr2 = array(
'post_id' => 12,
'content' => 'Some content is here too',
'created_at' => 1402154823
);
$posts = $arr2['created_at'] > $arr1['created_at']
? [$arr2, $arr1]
: [$arr1, $arr2];
But apparently what you're after is a way to sort the posts if they're in array of unknown length. In that case you should use uasort built-in PHP function, which allows to sort by user-defined function and maintains indexes in associative arrays (as opposed to plain usort). Example code would then look like this:
$posts = [$arr1, $arr2];
uasort($posts, function($a, $b)
{
return $b['created_at'] - $a['created_at'];
});
var_dump($posts);
which outputs:
array(2) {
[1]=>
array(3) {
["post_id"]=>
int(12)
["content"]=>
string(24) "Some content is here too"
["created_at"]=>
int(1402154823)
}
[0]=>
array(3) {
["id"]=>
int(1)
["text"]=>
string(17) "Some text is here"
["created_at"]=>
int(130458750)
}
}
To get reverse order you may just reverse arguments in custom sort function, i.e. swap $a with $b.

Answer 2

Combining rr-'s solution, I came up with the following:
$arr1 = array(
'id' => 1,
'text' => 'Some text is here',
'timestamp' => 130458750
);
$arr2 = array(
'post_id' => 12,
'content' => 'Some content is here too',
'created_at' => 1402154823
);
$arr3 = array(
'post_id' => 21,
'content' => 'Some content is here too',
'created_at' => 1258475
);
$arr = [];
$arr[] = $arr1;
$arr[] = $arr2;
$arr[] = $arr3;
uasort($arr, function($a, $b)
{
$t1 = isset($a['timestamp']) ? $a['timestamp'] : $a['created_at'];
$t2 = isset($b['timestamp']) ? $b['timestamp'] : $b['created_at'];
return $t2 - $t1
});
var_dump($arr);
It sorts the arrays even when the keys are different.