如何在一个datagridcolumn中连接两个数据字段？

dataGridColumn

    [Bindable]private var myDataProvider:ArrayCollection = new ArrayCollection([
                            {fname: \'fname 1\', lname: \'lname 1\'},
                            {fname: \'fname 2\', lname: \'lname 2\'},
                            {fname: \'fname 3\', lname: \'lname 3\'}
                        ]);

    private function myLabelFunction(item:Object, column:DataGridColumn):String {
        return  item.fname + \' \' + item.lname;
    }

    <mx:DataGrid dataProvider=\"{myDataProvider}\">
        <mx:columns>
            <mx:DataGridColumn labelFunction=\"{myLabelFunction}\" headerText=\"Full Name\" />
        </mx:columns>
    </mx:DataGrid>

private function concat(item:Object, column:DataGridColumn):String
        {
            return (item.id+\"\"+item.catCode);

[Bindable]private var cat:ArrayCollection = new ArrayCollection();