package com.archfamily {
 
	import flash.events.Event;
	import flash.utils.Dictionary;
 
	import mx.collections.ArrayCollection;
	import mx.events.CollectionEvent;
 
	public class DedupeArrayCollection extends ArrayCollection {
 
		private var _dedupeProperty:String = "";
 
		public function set dedupeProperty( value:String ):void {
			_dedupeProperty = value;
			this.source = this.source;
		}
		public function get dedupeProperty():String {
			return _dedupeProperty;
		}
 
		/**
		 * 
		 * Needed to override the standard dataprovider in order to reset
		 * the duplicate value each time
		 * 
		 */
		override public function set source( value:Array ):void {
			var _returnArray:Array = value;
 
			if ( value && dedupeProperty.length > 0 ) {
				var _map:Dictionary = new Dictionary( true );
 
				value.forEach( function( item:*, index:int, array:Array ):void {
					_map[ item[ this ] ] = item; // in the loop, this == dedupeProperty
				}, dedupeProperty );
 
				_returnArray = [];
				for each ( var object:Object in _map ) {
					_returnArray.push( object );
				}
			}
 
			super.source = _returnArray;
		}
 
		public function DedupeArrayCollection( source:Array=null ) {
			super( source );
		}
 
	}
}

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" creationComplete="init()" xmlns:archfamily="com.archfamily.*">
	<mx:Script>
		<![CDATA[
			import com.archfamily.DedupeArrayCollection;
 
			[Bindable] private var ac:DedupeArrayCollection = new DedupeArrayCollection( [ { name: "car", total: 100 },{ name: "bus", total: 200 },{ name: "bike", total: 300 },{ name: "train", total: 200 },{ name: "boat", total: 400 },{ name: "car", total: 500 },{ name: "bus", total: 200 },{ name: "convertible", total: 100 },{ name: "gizmo", total: 300 },{ name: "boat", total: 300 },{ name: "car", total: 100 },{ name: "dune buggy", total:300 },{ name: "motorcycle", total: 100 }] );
 
			public function init():void {
				ac.dedupeProperty = "total";
			}			
		]]>
	</mx:Script>
	<mx:VBox>
		<mx:ComboBox id="testing" dataProvider="{ ac }" labelField="name" />
	</mx:VBox>
</mx:Application>