I have the following xml: <RowSet> <Row> <Number>12345</Number> <Quantity>42</Quantity> </Row> <Row> <Number>12345</Number> <Quantity>12</Quantity> </Row> <Row> <Number>54321</Number> <Quantity>37</Quantity> </Row> </RowSet> I want to use an xsl to combine the elements with the same Number and the resulting should sum the Quantity elements. So the output should look like this: <RowSet> <Row> <Number>12345</Number> <Quantity>64</Quantity> </Row> <Row> <Number>54321</Number> <Quantity>37</Quantity> </Row> </RowSet>