gistfile1.php

<?php
        $expert_parents = array( array( "parent_entry_id" => "1758" ), array( "parent_entry_id" => "151" ), );
	$topic_parents  = array( array( "parent_entry_id" => "151" ),
	                         array( "parent_entry_id" => "1815" ),
	                         array( "parent_entry_id" => "2548" ),
	                         array( "parent_entry_id" => "2550" ), );


	function find_matches( $val1, $val2 ) {
		return ( intval( $val1["parent_entry_id"] ) - intval( $val2["parent_entry_id"] ) );
	}

	$all_parents_assoc = array_uintersect( $topic_parents, $expert_parents,   'find_matches'  );

	var_dump( $all_parents_assoc );