Sort array by two object properties using anonymous function

Question

I have the following array:

Array
(
    [0] => stdClass Object
        (
            [timestamp] => 1
            [id] => 10
        )

    [1] => stdClass Object
        (
            [timestamp] => 123
            [id] => 1
        )

    [2] => stdClass Object
        (
            [timestamp] => 123
            [id] => 2
        )

) 

I'm currently using the following code to sort the array by the timestamp property:

function sort_comments_by_timestamp(&$comments, $prop)
{
    usort($comments, function($a, $b) use ($prop) {
        return $a->$prop < $b->$prop ? 1 : -1;
    });
}

How can I also sort id by id descending when timestamp is the same?

Answer 1

Suggestion is to send in an array with $props

function sort_comments_by_timestamp(&$comments, $props)
{
    usort($comments, function($a, $b) use ($props) {
        if($a->$props[0] == $b->$props[0])
            return $a->$props[1] < $b->$props[1] ? 1 : -1;
        return $a->$props[0] < $b->$props[0] ? 1 : -1;
    });
}

And then call it with

sort_comments_by_timestamp($unsorted_array,array("timestamp","id"));

If you want it to work with X number of $props you can make a loop inside the usort always comparing a property with its preceding property in the array like this:

function sort_comments_by_timestamp(&$comments, $props)
{
    usort($comments, function($a, $b) use ($props) {
        for($i = 1; $i < count($props); $i++) {
            if($a->$props[$i-1] == $b->$props[$i-1])
                return $a->$props[$i] < $b->$props[$i] ? 1 : -1;
        }
        return $a->$props[0] < $b->$props[0] ? 1 : -1;
    });
}

Cheers!

Answer 2

function sort_comments_by_timestamp(&$comments, $prop)
{
    usort($comments, function($a, $b) use ($prop) {
        if ($a->$prop == $b->$prop)
          return $b->id - $a->id;
        else
          return $a->$prop < $b->$prop ? 1 : -1;
    });
}

The above sorts first by the $prop parameter and then secondary by id.