I have the following fragment repeated mulitple times and need to sum the SKU_QUANTITY and transform the XML based upon a grouping of the SKU_TIE, SKU_NUMBER, and MFG_PART_NUM, ie display the resulting node-set where these element values are the same. 
<SKU_INFO>
    <DETAIL_SEQ_NUMBER>11</DETAIL_SEQ_NUMBER>
    <SKU_TIE>1</SKU_TIE>
    <SKU_NUMBER>223344</SKU_NUMBER>
    <SKU_QUANTITY>2</SKU_QUANTITY>
    <MFG_PART_NUM>1234A</MFG_PART_NUM>
    <ITEM_TYPE_CODE>N</ITEM_TYPE_CODE>
    <SKU_DESCRIPTION>SI,MOD</SKU_DESCRIPTION>
    <BASE_SKU_FLAG>y</BASE_SKU_FLAG>
  </SKU_INFO>
  <SKU_INFO>..........
I've attempted to do this with the xslt key() function however I've been unable to group these keys distinctively. Here's how I've delcared the keys and attempted the grouping
......

<xsl:key name="sku_tie" match="SKU_INFO" use="SKU_TIE" />
<xsl:key name="sku_num" match="SKU_INFO" use="SKU_NUMBER" />
<xsl:key name="part" match="SKU_INFO" use="MFG_PART_NUM" /> 
		<xsl:template match="/" >
  <!-- i'm not sure how to accomplish the grouping however with the keys....
   <xsl:for-each select="key('header_id', /CustomerOrder/headerID)" >
       <xsl:for-each select="key('sku_tie', SKU_TIE)" >  
        ........							
Any help is greatly appreciated
-- 
MEC6304