Use for-each-group to eliminate duplicate output nodes?

I have a transformation during which I'd like to eliminate some duplicate nodes 
which are generated in the transformation. Below is a sample of a portion of 
the input document the relevant templates from the XSLT document and the output 
currently generated.

I need to eliminate duplicate lines from the output file. If I were 
post-processing with perl, I'd use a hash to do this. Now that I'm moving into 
XSLT 2.0, I have the feeling that something similar to a perl hash can be got 
using <xsl:for-each-group>.

The actual stylesheet and data document are somewhat more complicated. I hope 
that I have steered correctly between the Scylla and Charybdis of too much and 
too little information. Can someone tell me whether <xsl:for-each-group> can be 
used like a perl hash to eliminate duplicate values, and if so how? Thanks.

-- Data Document (sample portion)--
<path>
<node type="process" id="023">
  <predecessors>
     <node type="process" id="020">
        <predecessors>
           <node type="process" id="001">
              <predecessors>
                 <node type="data-store" id="058"/>
              </predecessors>
           </node>
           <node type="process" id="002">
              <predecessors>
                 <node type="data-store" id="059"/>
              </predecessors>
           </node>
        </predecessors>
     </node>
  </predecessors>
</node>

<node type="process" id="024">
  <predecessors>
     <node type="process" id="020">
        <predecessors>
           <node type="process" id="001">
              <predecessors>
                 <node type="data-store" id="058"/>
              </predecessors>
           </node>
           <node type="process" id="002">
              <predecessors>
                 <node type="data-store" id="059"/>
              </predecessors>
           </node>
        </predecessors>
     </node>
   </predecessors>
</node>
</path>

These are the templates that process the part of the document shown.:

-- XSLT document --
<xsl:template match="/">
  digraph d{
  <xsl:apply-templates />
                }
</xsl:template>

<xsl:template match="path">
  node_<xsl:value-of select="node/@id" /> ;
  <xsl:apply-templates mode="set-nodes" />
  <xsl:apply-templates mode="set-connections" />
</xsl:template>

<xsl:template match="predecessors" mode="set-nodes">
  <xsl:apply-templates mode="set-nodes" />
</xsl:template>

<xsl:template match="node" mode="set-nodes">
  <xsl:apply-templates mode="set-nodes" />
</xsl:template>

<xsl:template match="predecessors/node" mode="set-nodes">
  node_<xsl:value-of select="@id" />
  <xsl:apply-templates mode="set-nodes" />
</xsl:template>

<xsl:template match="node" mode="set-connections">
  <xsl:variable name="target-node" select="." />
  <xsl:for-each select="predecessors/node">
    node_<xsl:value-of select="@id" /> -> node_<xsl:value-of 
select="$target-node/@id" />
  </xsl:for-each>
  <xsl:apply-templates mode="set-connections" />
</xsl:template>

Output from existing stylesheet (sorted to make identification of duplicates 
easier):

digraph d{
        node_001
        node_001
        node_002
        node_002
        node_003
        node_003
        node_004
        node_005
        node_006
        node_007
        node_008
        node_020
        node_020
        node_023
        node_024
        node_028
        node_038
        node_058
        node_058
        node_059
        node_059
        node_060
        node_061
        node_062
        node_063
        node_064
        node_065

        node_001 -> node_020
        node_001 -> node_020
        node_002 -> node_020
        node_002 -> node_020
        node_004 -> node_038
        node_005 -> node_038
        node_006 -> node_038
        node_007 -> node_038
        node_008 -> node_038
        node_020 -> node_023
        node_020 -> node_024
        node_023 -> node_038
        node_024 -> node_038
        node_038 -> node_028
        node_058 -> node_001
        node_058 -> node_001
        node_059 -> node_002
        node_059 -> node_002
        node_060 -> node_003
        node_061 -> node_004
        node_062 -> node_005
        node_063 -> node_006
        node_064 -> node_007
        node_065 -> node_008
}
-- 
Charles Knell
cknell(_at_)onebox(_dot_)com - email

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