How to summarize a String Field ?

[YouPeng Yang]

Hi

   One of my filed called AMOUNT  is  String,and I want to  calculate the
sum of the this filed.
    I have try it with the stats component,it only give out the stats
information without sum item just as following:

<lst name="AMOUNT">
     <str name="min">000000000000</str>
     <str name="max">500000000000</str>
     <long name="count">24230</long>
     <long name="missing">26362</long>
      <lst name="facets"/>
</lst>

   Is there any ways to achieve this object?

Regards