Using aggregation in xslt to display sum of rows after grouping in CQWP

Question

there is a list in SP which has employee name, project name, and weightage. now there is a requirement to produce a customized view in CQWP where data is grouped by project there must be 2 columns one for projects and other for SUM of percentage of each
row in each project. In header i have a template as no text which hides the text. and in itemstyle.xsl i have made a template as mystyle which makes columns and displays data. i just need to add SUM of each row of a project and display it together with project
and the rows must not be shown.
<xsl:template name="MyStyle" match="Row[@Style='MyStyle']" mode="itemstyle">
<table border='1'>
<tr>
<td><h2>Project</h2></td>
<td><h2>Percentage</h2></td>
</tr>
<tr>
<td colspan="1"><h3><xsl:value-of select="@Project" /></h3></td>
<td>
<xsl:value-of disable-output-escaping="yes" select="@Percentage" />
</td>
</tr>
</table>
</xsl:template>
I am not able to figure out how to aggregate this thing. need help!

Answer 1

thanks again, one more Q.
in XSLT mapping i have written for loop for complete structure.
example : <Details>
                     <node1>
                     <node2>
               </details>
in XSLT mapping
                     <xsl:for-each select="ZMATMAS_01/IDOC/E1MARAM">
     <Details>
     </Details>
     </xsl:for-each>
if i add the field at target side....then i will come under details node and it will be repeated.
how to declare in XSLT mapping.