I have a nodeset which consists of 'value' elements like above. I want
  to get a nodeset of B elements whose key values are same.(e.g. all the
  value elements'(in this nodeset) B elements whose keys are 'USD'.) 
  if nodeset is -> tempnodeset

  how should i define the select clause and the key?

  
As you said yourself:

select="$tempnodeset/B[key='USD']


  But the grouping with the key does not work.

You'd need to give more information about what grouping you are trying
to do and what doesn't work.

David

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