How to differentiate between display value and id value using the jQuery UI Autocomplete plugin with remote data source?

I have a search box in my application that uses the jQuery UI Autocomplete plugin to display a list of users in the system based on last name, from a remote data source.

When a user is clicked from the autocomplete list, I'd like the browser to redirect to that user's individual page (based on a GET parameter). However, the GET parameter for the user page is the user "id", different from the display values "last_name, first_name".

How do I push the user "id" to the GET parameter while still displaying the first and last names values in the dropdown?

I have seen similar questions asked on here, but none while using a remote data source.

Any help you can provide, would be amazing!

Javascript:

$(document).ready(function() {

    $( ".user_autocomplete" ).autocomplete({
            source: "../../db/users.php",
            minLength: 0,
            focus: function (event, ui) {
                this.value = ui.item.value;
            },          
    }).bind( "autocompleteselect", function(event, ui) {
        window.location.href = "/users/index.php?id=" + this.value;
    });

});  

Remote Data Source (users.php)

<?php

$return_arr = array();

if(isset($_GET['term'])) {
    $mysearchString = $_GET['term'];
}

$sth = $dbh->query("SELECT id, first_name, last_name FROM users
                    WHERE last_name LIKE '$mysearchString%'
                    ORDER BY last_name");

while ($row = $sth->fetch ()) { 

    $row_array = $row['last_name'].', '.$row['first_name'];

    array_push($return_arr,$row_array); 

}

echo json_encode($return_arr);

?>

To have an ID that is different from the (display) VALUE, you must return a JSON encoded array of objects like this:

[
   {
      "id":"1",
      "value":"Doe, John"
   },
   {
      "id":"2",
      "value":"Smith, Mary"
   }
]

You can then use ui.item.id to retrieve the selected ID.

NOTE: You can also provide a "label" property that is different from the "value" property. Here's the information from the documentation:

The local data can be a simple Array of Strings, or it contains Objects for each item in the array, with either a label or value property or both. The label property is displayed in the suggestion menu. The value will be inserted into the input element after the user selected something from the menu. If just one property is specified, it will be used for both, eg. if you provide only value-properties, the value will also be used as the label.

EDIT:

I'm not a PHP guy, but I imagine the code to create the JSON array would be something like this:

<?php
$return_arr = array();

    ... snip ...

while ($row = $sth->fetch ()) { 
    $row_array = array(
        "id" => $row['id'], 
        "value" => $row['last_name'].', '.$row['first_name']
    );
    array_push($return_arr, $row_array); 
}
echo json_encode($return_arr);
?>