I have this file, but i'd like change whith xslt....
<?xml version="1.0"?>
<NewDataSet>
  <authors>
    <name>Johnson</name>
    <salary>10</salary>
    <country>France</country>
  </authors>
  <authors>
    <name>David</name>
    <salary>10</salary>
    <country>France</country>
  </authors>
  <authors>
    <name>Richard</name>
    <salary>10</salary>
    <country>Germany</country>
  </authors>
  <authors>
    <name>Lisa</name>
    <salary>1000</salary>
    <country>Germany</country>
  </authors>
  <authors>
    <name>Harry</name>
    <salary>10</salary>
    <pais>Francia</pais>
    <salary>1000</salary>
    <country>Germany</country>
  </authors>
</NewDataSet>


to transform this new xml grouping by country with the totally of the
salary of this groups depends on country

<?xml version="1.0"?>
<NewDataSet>
  <authors>
    <name>Johnson</name>
    <salary>10</salary>
    <country>France</country>
  </authors>
  <authors>
    <name>David</name>
    <salary>10</salary>
    <country>France</country>
  </authors>
  <salaryGroup>
  	<salary>20</salary>
    <country>France</country>
  </salaryGroup>
  <authors>
    <name>Richard</name>
    <salary>10</salary>
    <country>Germany</country>
  </authors>
  <authors>
    <name>Lisa</name>
    <salary>1000</salary>
    <country>Germany</country>
  </authors>
  <authors>
    <name>Harry</name>
    <salary>10</salary>
    <pais>Francia</pais>
    <salary>1000</salary>
    <country>Germany</country>
  </authors>
  <salaryGroup>
  	<salary>2010</salary>
    <country>Germany</country>
  </salaryGroup>
</NewDataSet>

thank you very much