<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white"
        creationComplete="init()" viewSourceURL="srcview/index.html">

    <mx:Script>
        <![CDATA[
            private var keys:Object = {};

            /**
             * Called by the Application container's creationComplete
             * event handler. This method creates a new Array object
             * which will be used as a data provider as well as a
             * filtered view of that array which does not contain
             * duplicated items.
             */
            private function init():void {
                /* Create a dummy data source with some semi-random
                    data. */
                var arr:Array = [];
                arr.push({data:1, label:"one"});
                arr.push({data:1, label:"one"});
                arr.push({data:1, label:"one"});
                arr.push({data:1, label:"one"});
                arr.push({data:2, label:"two"});
                arr.push({data:2, label:"two"});
                arr.push({data:2, label:"two"});
                arr.push({data:1, label:"one"});
                arr.push({data:3, label:"three"});
                arr.push({data:3, label:"three"});

                /* Filter the original array and call the
                    removeDuplicates() function on each item
                    in the array. */
                var filteredArr:Array = arr.filter(removedDuplicates);

                arrColl.source = arr;
                dedupedArrColl.source = filteredArr;
            }

            /**
             * This method is used to filter an array so that no
             * duplicate items are created. It works by first
             * checking to see if a keys object already contains
             * a key equal to the current value of the item.data
             * value. If the key already exists, the  current item
             * will not be readded to the data provider. If the key
             * does not already exist, add the key to the keys
             * object and add this item to the data provider.
             */
            private function removedDuplicates(item:Object, idx:uint, arr:Array):Boolean {
                if (keys.hasOwnProperty(item.data)) {
                    /* If the keys Object already has this property,
                        return false and discard this item. */
                    return false;
                } else {
                    /* Else the keys Object does *NOT* already have
                        this key, so add this item to the new data
                        provider. */
                    keys[item.data] = item;
                    return true;
                }
            }
        ]]>
    </mx:Script>

    <mx:ArrayCollection id="arrColl" />
    <mx:ArrayCollection id="dedupedArrColl" />

    <mx:HBox>
        <mx:VBox>
            <mx:Label text="Original ({arrColl.length} items):" />
            <mx:List dataProvider="{arrColl}" />
        </mx:VBox>
        <mx:VBox>
            <mx:Label text="Filtered ({dedupedArrColl.length} items):" />
            <mx:List dataProvider="{dedupedArrColl}" />
        </mx:VBox>
    </mx:HBox>

</mx:Application>