An XSLT equivalent of the SQL SUM and GROUP BY operati

Can anyone suggest how I might go about performing a transformation which is
the logical equivalent of a SQL statement like :

	SELECT Account, Date, SUM(Amount)
	FROM ...
	GROUP BY Account, Date

An example of the type of transformation I am trying to achieve (which
matches the above SQL) is given below. 

XML input :
<line>
<Account>64001</Account><Date>01/02/91</Date><Amount>50</Amount>
</line>
<line>
<Account>64001</Account><Date>01/02/91</Date><Amount>70</Amount>
</line>
<line>
<Account>64002</Account><Date>12/03/91</Date><Amount>60</Amount>
</line>
<line>
<Account>64002</Account><Date>01/02/91</Date><Amount>30</Amount>
</line>
<line>
<Account>64002</Account><Date>12/03/91</Date><Amount>90</Amount>
</line>

XML output :
<line>
<Account>64001</Account><Date>01/02/91</Date><Amount>120</Amount>
</line>
<line>
<Account>64002</Account><Date>01/02/91</Date><Amount>30</Amount>
</line>
<line>
<Account>64002</Account><Date>12/03/91</Date><Amount>150</Amount>
</line>

The transformation should sum all the Amounts for each matching Date within
each matching Account (i.e. Account 64001 shrinks to a single line as both
the dates are the same, but Account 64002 shrinks to two lines - one with
the sum of the amounts for 01/02/91 and one with the sum of the amounts for
12/03/91).

Any hints/suggestions/solutions for the specific example quoted or a more
generic solution (where parameters specify the nodes to group by and their
precedence) would be gratefully appreciated.


 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list