WordPress: Sort an array of post objects by any property, remove duplicates, and use post ids as the key in the returned array.

gistfile1.aw

<?php
function sort_posts( $posts, $orderby, $order = 'ASC', $unique = true ) {
	if ( ! is_array( $posts ) ) {
		return false;
	}
	
	usort( $posts, array( new Sort_Posts( $orderby, $order ), 'sort' ) );
	
	// use post ids as the array keys
	if ( $unique && count( $posts ) ) {
		$posts = array_combine( wp_list_pluck( $posts, 'ID' ), $posts );
	}
	
	return $posts;
}

class Sort_Posts {
	var $order, $orderby;
	
	function __construct( $orderby, $order ) {
		$this->orderby = $orderby;
		$this->order = ( 'desc' == strtolower( $order ) ) ? 'DESC' : 'ASC';
	}
	
	function sort( $a, $b ) {
		if ( $a->{$this->orderby} == $b->{$this->orderby} ) {
			return 0;
		}
		
		if ( $a->{$this->orderby} < $b->{$this->orderby} ) {
			return ( 'ASC' == $this->order ) ? -1 : 1;
		} else {
			return ( 'ASC' == $this->order ) ? 1 : -1;
		}
	}
}
?>

For anyone looking to specifically sort WP Post objects, you can also use the WordPress function wp_list_sort