Question

I have this input XML which needs to be transformed with an xslt

<root>
    <node id="a">
        <section id="a_1" method="run">
            <item id="0">
                <attribute>
                    <color>Red</color>
                </attribute>
            </item>
        </section>
        <section id="a_2">
            <item id="0">
                <attribute>
                    <color>Red</color>
                </attribute>
            </item>
        </section>
        <section id="a_1" method="run">
            <item id="0">
                <attribute>
                    <color>Red</color>
                </attribute>
            </item>
        </section>
    </node>
    <node id="b">
        <section id="b_1" method="create">
            <user id="b_1a">
                <attribute>
                    <name>John</name>
                </attribute>
            </user>
            <user id="b_1b">
                <attribute>a</attribute>
            </user>
        </section>
        <section id="b_1" method="create">
            <user id="b_1c">
                <attribute>a</attribute>
            </user>
        </section>
        <section id="b_2">
            <user id="b_1a">
                <attribute>
                    <name>John</name>
                </attribute>
            </user>
        </section>
    </node>
</root>

Expected output:

<root>
    <node id="a">
        <section id="a_1">
            <item id="0">
                <attribute>
                    <color>Red</color>
                </attribute>
            </item>
        </section>
        <section id="a_2">
            <item id="0">
                <attribute>
                    <color>Red</color>
                </attribute>
            </item>
        </section>
    </node>
    <node id="b">
        <section id="b_1" method="create">
            <user id="b_1a">
                <attribute>
                    <name>John</name>
                </attribute>
            </user>
            <user id="b_1b">
                <attribute>a</attribute>
            </user>
        </section>

        <section id="b_2">
            <user id="b_1a">
                <attribute>
                    <name>John</name>
                </attribute>
            </user>
        </section>
    </node>
</root>

It does not matter which node will be eliminated, as long as it has the same element name, id and method, one of them will be removed.
Any idea what the xsl looks like ?

Note: the element name can be anything doesn’t have to be and it has more than one element name in the whole file; as long as it has the same element name, id and attribute (ex. method=create) one of them will be eliminated.

Thanks very much.
cheers,
John

Answer 1

I. Here is a short and efficient (using keys) XSLT 1.0 transformation:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>
 <xsl:strip-space elements="*"/>

 <xsl:key name="kElemWithAttribs" match="*[@id and @method]"
  use="concat(name(), '+', @id, '+', @method)"/>

 <xsl:template match="node()|@*">
     <xsl:copy>
       <xsl:apply-templates select="node()|@*"/>
     </xsl:copy>
 </xsl:template>

 <xsl:template match=
  "*[@id and @method
    and
     not(generate-id()
        =
         generate-id(key('kElemWithAttribs',
                         concat(name(), '+', @id, '+', @method)
                         )[1]
                    )
         )
     ]"/>
</xsl:stylesheet>

When this transformation is applied on the provided XML document:

<root>
    <node id="a">
        <section id="a_1" method="run">
            <item id="0">
                <attribute>
                    <color>Red</color>
                </attribute>
            </item>
        </section>
        <section id="a_2">
            <item id="0">
                <attribute>
                    <color>Red</color>
                </attribute>
            </item>
        </section>
        <section id="a_1" method="run">
            <item id="0">
                <attribute>
                    <color>Red</color>
                </attribute>
            </item>
        </section>
    </node>
    <node id="b">
        <section id="b_1" method="create">
            <user id="b_1a">
                <attribute>
                    <name>John</name>
                </attribute>
            </user>
            <user id="b_1b">
                <attribute>a</attribute>
            </user>
        </section>
        <section id="b_1" method="create">
            <user id="b_1c">
                <attribute>a</attribute>
            </user>
        </section>
        <section id="b_2">
            <user id="b_1a">
                <attribute>
                    <name>John</name>
                </attribute>
            </user>
        </section>
    </node>
</root>

the wanted, correct result is produced:

<root>
   <node id="a">
      <section id="a_1" method="run">
         <item id="0">
            <attribute>
               <color>Red</color>
            </attribute>
         </item>
      </section>
      <section id="a_2">
         <item id="0">
            <attribute>
               <color>Red</color>
            </attribute>
         </item>
      </section>
   </node>
   <node id="b">
      <section id="b_1" method="create">
         <user id="b_1a">
            <attribute>
               <name>John</name>
            </attribute>
         </user>
         <user id="b_1b">
            <attribute>a</attribute>
         </user>
      </section>
      <section id="b_2">
         <user id="b_1a">
            <attribute>
               <name>John</name>
            </attribute>
         </user>
      </section>
   </node>
</root>

Explanation:

Using the Muenchian method for grouping with a composite key. Here we ignore (delete) every node that isn’t the first in a group.

---

II. XSLT 2.0 solution — even shorter and not less efficient:

<xsl:stylesheet version="2.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output omit-xml-declaration="yes" indent="yes"/>

 <xsl:template match="node()|@*">
     <xsl:copy>
       <xsl:apply-templates select="node()|@*"/>
     </xsl:copy>
 </xsl:template>

 <xsl:template match="node">
  <xsl:copy>
    <xsl:apply-templates select="@*"/>

    <xsl:for-each-group select="*"
         group-by="concat(name(), '+', @id, '+', @method)">
      <xsl:apply-templates select="."/>
    </xsl:for-each-group>
  </xsl:copy>
 </xsl:template>
</xsl:stylesheet>

Explanation:

Proper use of xsl:for-each-group with a group-by attribute.