With some work I have been able to get all the distinct values but I
don't know how to get only first 8 distinct values :

My XSL goes something like this :

<xsl:apply-templates select="//HIT[generate-id(.) =
generate-id(key('hit-keyword',
substring-after(substring-before(substring-before(FIELD[@NAME='docvector']
,'1]'),','),'['))[1])]" mode="col"/>

<xsl:apply-templates select="//HIT[generate-id(.) =
 generate-id(key('hit-keyword',
 substring-after(substring-before(substring-before(FIELD[@NAME='docvector']
 ,'1]'),','),'['))[1])][position() &lt;= 8]" mode="col"/>

cheers
andrew