How to get unique data

Hi,
    In SQL "Select Distinct ...." can get the unique data form the specify table. But in xml I can not do the same work.

    The data is as following:
    <prog pid="0">
        <item iid="0" fid="1"/>
        <item iid="0" fid="2"/>
        <item iid="0" fid="3"/>
        <item iid="0" fid="4"/>
        <item iid="0" fid="5"/>
        <item iid="1" fid="6"/>
        <item iid="1" fid="7"/>
        <item iid="1" fid="8"/>
        <item iid="1" fid="9"/>
        <item iid="1" fid="10"/>
    </prog>
    <prog pid="1">
        <item iid="2" fid="11"/>
        <item iid="2" fid="12"/>
        <item iid="2" fid="13"/>
        <item iid="2" fid="14"/>
        <item iid="2" fid="15"/>
        <item iid="3" fid="16"/>
        <item iid="3" fid="17"/>
        <item iid="3" fid="18"/>
        <item iid="3" fid="19"/>
        <item iid="3" fid="20"/>
    </prog>

    How can I use xsl in IE to get the follow data:
    <prog pid="0">
        <item iid="0" fid="1"/>
        <item iid="1" fid="6"/>
    </prog>
    <prog pid="1">
        <item iid="2" fid="11"/>
        <item iid="3" fid="16"/>
    </prog>

    fid attribute's value here is not important, I just want to the first item element with the unique iid.

    I use the follow xsl
    ...
    <xsl:for-each select="//prog" order-by="@pid">
    <xsl:for-each select="item" order-by="@iid">
    <xsl:if exp="!checkDup( @iid )">
    ...show the unique data...
    </xsl:if>
    </xsl:for-each>
    </xsl:for-each>
    ...
    <xsl:script language="javascript">
    <![CDATA[
    var arrItemName = new Array();

    function checkDup( item )
    {
	var isDup = false;

	for ( i = 0; i&lt;arrItemName.length; i++ )
	{
		if ( arrItemName[i] == item ){
			isDup = true;
			break;
		}
	}

	if ( isDup==false ){
		var len = arrItemName.length;
		arrItemName.length ++;
		arrItemName[len] = item;
	}

	return isDup;
    }
    ]]>
    </xsl:script>

    IE reported no error but still give the duplicate data, why??? Can anyone help me out???
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