PHP Merge & Sort Several Different Arrays of Objects

You can leverage usort for the sorting, as long as each object has a public timestamp field

function compareObjTimestamps( $a, $b ) {
    return $a->timestamp - $b->timestamp;
}

usort( $objArray, 'compareObjTimestamps' );

For the merging, following this approach just lump all of the objects into a single array prior to the call to usort.

Example

<?php

class A {
    public $sortField;

    public function __construct( $sortField ) {
        $this->sortField = $sortField;
    }
}

class B {
    public $sortField;

    public function __construct( $sortField ) {
        $this->sortField = $sortField;
    }

}

function compare( $a, $b ) {
    return $a->sortField - $b->sortField;
}


$test = array(
    new A(1),
    new B(2),
    new A(3),
    new B(4),
    new B(1),
    new A(17),
    new B(10),
);

usort( $test, 'compare' );

foreach( $test as $entry ) {
    echo $entry->sortField . ': ' . get_class( $entry ) . "\n";
}

Multiple iterations of this script produced the following output:

1: B 
1: A 
2: B 
3: A 
4: B 
10: B 
17: A

So it looks like that whatever appears later in the input will be first in the output, although I can't find any documentation on this. The manual simply states:

4.1.0 A new sort algorithm was introduced. The cmp_function doesn't keep the original order for elements comparing as equal.