Q:

PHP order array by date?

Possible Duplicate:
PHP Sort a multidimensional array by element containing date 

I have some data from XML or JSON in a PHP array that looks like this:
[0]= array(2) {
    ["title"]= string(38) "Another title"
    ["date"]= string(31) "Fri, 17 Jun 2011 08:55:57 +0200"
}
[1]= array(2) {
    ["title"]= string(38) "My title"
    ["date"]= string(31) "Mon, 16 Jun 2010 06:55:57 +0200"
}

What I want to do is order the two items by date.

Is it possible to sort by date, when the sort value is inside every item?
Do I need to convert the date format to timestamp?

What I don't want to do
I could use date and set it as the ID but that don't feel right, because two items can have the same date and then it would not be unique.

A:

You don't need to convert your dates to timestamp before the sorting, but it's a good idea though because it will take more time to sort without it.
$data = array(
    array(
        "title" => "Another title",
        "date"  => "Fri, 17 Jun 2011 08:55:57 +0200"
    ),
    array(
        "title" => "My title",
        "date"  => "Mon, 16 Jun 2010 06:55:57 +0200"
    )
);

function sortFunction( $a, $b ) {
    return strtotime($a["date"]) - strtotime($b["date"]);
}
usort($data, "sortFunction");
var_dump($data);

A:

Use usort:
usort($array, function($a1, $a2) {
   $v1 = strtotime($a1['date']);
   $v2 = strtotime($a2['date']);
   return $v1 - $v2; // $v2 - $v1 to reverse direction
});

A:

I recommend using DateTime objects instead of strings, because you cannot easily compare strings, which is required for sorting. You also get additional advantages for working with dates.
Once you have the DateTime objects, sorting is quite easy:
usort($array, function($a, $b) {
  return ($a['date'] < $b['date']) ? -1 : 1;
});

