[xsl] Keys and select distinct - is that the solution ?

I've been struggling with a problem for several hours now, and I
cannot find the solution:
I have an XML document with a elements grouped in elements and
ManureTypeCodes and datavalues as siblings.
Then I have - somewhere else - in the document lookup information
(labels) for the codes.
These are grouped in elements of ManureTypeCodes and ManureTypeNames

I want to create a template rule which matches the codes and looks up
the corresponding name and ONLY writes the
ManureTypeName out once! In RDBMS I would use something like select
distinct when selecting the codes, but I dont know what the right
approach is in XSLT.

my XML:
<eih>
   <!-- Codes and data  -->
   <eih:ManureTypeCollection>
       <eih:ManureTypeStructure>
           <gr:ManureTypeCode>5</gr:ManureTypeCode>
           <gr:ElementIdentifier>N</gr:ElementIdentifier>
           <gr:ElementQuantity>17.0</gr:ElementQuantity>
       </eih:ManureTypeStructure>
       <eih:ManureTypeStructure>
           <gr:ManureTypeCode>5</gr:ManureTypeCode>
           <gr:ElementIdentifier>P</gr:ElementIdentifier>
           <gr:ElementQuantity>0.6</gr:ElementQuantity>
       </eih:ManureTypeStructure>
       <eih:ManureTypeStructure>
           <gr:ManureTypeCode>4</gr:ManureTypeCode>
           <gr:ElementIdentifier>N</gr:ElementIdentifier>
           <gr:ElementQuantity>17.5</gr:ElementQuantity>
       </eih:ManureTypeStructure>
       <eih:ManureTypeStructure>
           <gr:ManureTypeCode>4</gr:ManureTypeCode>
           <gr:ElementIdentifier>P</gr:ElementIdentifier>
           <gr:ElementQuantity> 6.3</gr:ElementQuantity>
       </eih:ManureTypeStructure>
   </eih:ManureTypeCollection>

   <!-- look up information for the codes -->
   <eih:XImanureTypeCollection>
       <eih:XImanureTypeStructure>
           <gr:ManureTypeCode>4</gr:ManureTypeCode>
           <gr:ManureTypeName>Fast gxdning</gr:ManureTypeName>
       </eih:XImanureTypeStructure>
       <eih:XImanureTypeStructure>
           <gr:ManureTypeCode>5</gr:ManureTypeCode>
           <gr:ManureTypeName>Ajle</gr:ManureTypeName>
       </eih:XImanureTypeStructure>
       <eih:XImanureTypeStructure>
   </eih:XImanureTypeCollection>
</eih>

Christian Rasmussen
Denmark