Jquery Autocomplete using XML - grab alternate result

I have the following jquery Autocomplete form that pulls data in from a local XML file.

It works fine and displays the data as it should, but how can I return a specific data value into the search field?

For example, when searching for London, the auto complete returns values thus:

London Heathrow Airport, UK -

Which is great - BUT I'd like it populate the actual search field by grabbing a specific XML ID, (The airport code = IATA) and add ONLY that to the search field - like this:

LHR

How can I a开发者_Go百科chieve that ?

Here's the jquery code

@Nicola Peluchetti

Thanks for your help and answer - this is what I got from your comments - but it's not working - did I miss something ?

$(document).ready(function() {
    var myArr = [];

    $.ajax({
        type: "GET",
        url: "airports.xml", 
        dataType: "xml",
        success: parseXml,
        complete: setupAC,
        failure: function(data) {
            alert("XML File could not be found");
            }
    });

function parseXml(xml)
{
//find every query value
    $(xml).find("state").each(function()
{
    //you are going to create an array of objects
    var thisItem = {};
    var thisItem[label] = $(this).attr("label") + ',  ' + $(this).attr("country");
    var thisItem[value] = $(this).attr("iata");
    myArr.push(thisItem);
});
} 



    function setupAC() {
        $("#city").autocomplete({
                source: myArr,
                minLength: 3,
                select: function(event, ui) {
            //replace the label with the value
            $(this).val(ui.value);
        }



        });
    }
});

and here's the airports.xml file snippet

<states>
<state label="London Heathrow" iata="LHR" country="UK" />
<state label="Syndey" iata="SYD" country="Australia" />

....

And the search form snippet

<label for="city">From</label></td>

EDIT (i modified the answer according to the comments) - You could modify this function:

function parseXml(xml)
{
    //find every query value
        $(xml).find("state").each(function()
    {
        //you are going to create an array of objects
        var thisItem = {};
        thisItem['label'] = $(this).attr("label") + ',  ' + $(this).attr("country");
        thisItem['value'] = $(this).attr("iata");
        myArr.push(thisItem);
    });
} 

EDIT 2 - you don't need this second part: autocomplete automatically replace the "label" with the "value" if you specify both of them in the object

semplified fiddle here : http://jsfiddle.net/7cLxD/1/

In this case you must change your select function:

select: function(event, ui) {
    // here you are adding the full string:
    // `London Heathrow Airport, UK`, as .value
    $("#city").val(ui.item.value);
    // here you are adding the full string:
    // `LHR`, as .id
    $("#city").val(ui.item.id);

    $("#qf").submit();
}

But for this approach, you must change your way to create list.
More information with complete code you can see Autocomplete demo with xml data.