Recursive XSLT: Concat Multiple Nodes

Sharing this XSLT which I used couple of years back to concat a node set. The usecase was to extract a specific node set and concatenate their values.

Sample Input:

<root>
    <node>
        <data>123</data>
        <data>456</data>
        <junk>abc</junk>
    </node>
    <junknode>
        <junk>def</junk>
    </junknode>
    <node>
        <data>789</data>
        <junk>ghi</junk>
        <data>012</data>
    </node>
</root>

Desired Output:

<out>
  <mssg>123456789012</mssg>
  <junk>abcdefghi</junk>
</out>

XSLT:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:output indent="yes" />
  <xsl:template match="/">
    <out>
      <xsl:variable name="mssg_data">
        <xsl:call-template name="ConCat">
          <xsl:with-param name="List" select="/root/node/data" />
        </xsl:call-template>
      </xsl:variable>
      <xsl:variable name="junk_data">
        <xsl:call-template name="ConCat">
          <xsl:with-param name="List" select="//junk" />
        </xsl:call-template>
      </xsl:variable>
      <mssg>
        <xsl:value-of select="$mssg_data" disable-output-escaping="no" />
      </mssg>
      <junk>
        <xsl:value-of select="$junk_data"/> 
      </junk>
    </out>
  </xsl:template>
  <xsl:template name="ConCat">
    <xsl:param name="List" />
    <xsl:param name="result" select="''" />
    <xsl:choose>
      <xsl:when test="$List">
        <xsl:call-template name="ConCat">
          <xsl:with-param name="List" select="$List[position() &gt; 1]" />
          <xsl:with-param name="result" select="concat($result, $List[1])" />
        </xsl:call-template>
      </xsl:when>
      <xsl:otherwise>
        <xsl:value-of select="$result" disable-output-escaping="no" />
      </xsl:otherwise>
    </xsl:choose>
  </xsl:template>
</xsl:stylesheet>

Note: The similar result can be achieved by using XPATH evaluator to get text of data node set (ie /root/node/data/text()), depending on the requirement one or the other approach may be more suitable.

Looping in XSLT: Recursive Template Calls

To loop in XSLT you need to call a template recursively.

In past I have done this using two approaches:

Option-1: While Loop
Logic is similar to a while loop. So the counter is decremented till it is greater than 0.
 

 
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:output indent="no" />
  <xsl:template match="/">
    <LoopInput>
      <xsl:call-template name="CreateLoop">
        <xsl:with-param name="count" select="${numLoop}" />
      </xsl:call-template>
    </LoopInput>
  </xsl:template>
  <xsl:template name="CreateLoop">
    <xsl:param name="count" />
    <xsl:if test="$count &gt; 0">
      <xsl:call-template name="CreateLoop">
        <xsl:with-param name="count" select="$count - 1" />
      </xsl:call-template>
      <Line>
        <xsl:text disable-output-escaping="no">Line Data: </xsl:text>
        <xsl:value-of select="$count" disable-output-escaping="no" />
      </Line>
    </xsl:if>
  </xsl:template>
</xsl:stylesheet>

Option-2: For Loop
Here counter is incremented from a initial count till it reaches the desired loop count.

 
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:output indent="no" />
  <xsl:template match="/">
    <LoopInput>
      <xsl:call-template name="CreateLoop">
        <xsl:with-param name="MaxLoop" select="${numLoop}" />
        <xsl:with-param name="iLoop" select="1" />
      </xsl:call-template>
    </LoopInput>
  </xsl:template>
  <xsl:template name="CreateLoop">
    <xsl:param name="MaxLoop" />
    <xsl:param name="iLoop" />
    <Line>
      <xsl:text disable-output-escaping="no">Line Data: </xsl:text>
      <xsl:value-of select="$iLoop" disable-output-escaping="no" />
    </Line>
    <xsl:if test="$iLoop &lt; $MaxLoop">
      <xsl:call-template name="CreateLoop">
        <xsl:with-param name="MaxLoop" select="$MaxLoop" />
        <xsl:with-param name="iLoop" select="$iLoop + 1" />
      </xsl:call-template>
    </xsl:if>
  </xsl:template>
</xsl:stylesheet>