Question

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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.

1. Is it possible to sort by date, when the sort value is inside every item?
2. 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.

Answer 1

You don’t need to convert your dates to timestamps before the sorting, but it’s a good idea though because it will take more time to sort without this step.

$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);

Update

In newer PHP versions you can use arrow functions too. Here you can find a more concise version of the above:

usort($data, fn ($a, $b) => strtotime($a["date"]) - strtotime($b["date"]));