RE: Counting nodes efficiently

In this and similar problems one can re-use the identity transformation,
which processes strictly one node at a time (would a native English
speaker, please, suggest a good name? The best I could arrive at was "one
node at a time identity transformation"):

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

  <xsl:template match="@* | node()">
    <xsl:copy>
      <xsl:apply-templates select="@*"/>
      <xsl:apply-templates select="node()[1]"/>
    </xsl:copy>
    <xsl:apply-templates select="following-sibling::node()[1]"/>
  </xsl:template>

</xsl:stylesheet>

Cheers,
Wendell

This transformation produces the same results as the more well-known
identity rule.

The difference is that we now have the finest possible grain-level of
controll as every xsl:apply-templates instruction above always selects at
most one node.

It is trivial to add parameters and to override the one-at-a-time identity
for elements. Thus we finally have:

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

  <xsl:template match="@* | node()">
    <xsl:param name="pnAncestors" select="0"/>
    <xsl:param name="pnPreceding" select="0"/>
    <xsl:copy>
      <xsl:apply-templates select="@*"/>
      <xsl:apply-templates select="node()[1]">
        <xsl:with-param name="pnAncestors"
                        select="$pnAncestors+1"/>
        <xsl:with-param name="pnPreceding"
                        select="$pnPreceding"/>
      </xsl:apply-templates>
    </xsl:copy>
    <xsl:apply-templates select="following-sibling::node()[1]">
      <xsl:with-param name="pnAncestors"
                      select="$pnAncestors"/>
      <xsl:with-param name="pnPreceding"
                      select="$pnPreceding+1"/>

    </xsl:apply-templates>
  </xsl:template>

  <xsl:template match="*">
    <xsl:param name="pnAncestors" select="0"/>
    <xsl:param name="pnPreceding" select="0"/>

    <xsl:copy>
      <xsl:copy-of select="@*"/>
      <xsl:attribute name="_id">
        <xsl:value-of select=
                    "concat(name(), '_',
                            $pnAncestors, '_',
                            $pnPreceding
                            )"/>
      </xsl:attribute>
    </xsl:copy>
    <xsl:apply-templates select="node()[1]">
      <xsl:with-param name="pnAncestors"
                      select="$pnAncestors+1"/>
      <xsl:with-param name="pnPreceding"
                      select="$pnPreceding"/>
    </xsl:apply-templates>
    <xsl:apply-templates select="following-sibling::node()[1]">
      <xsl:with-param name="pnAncestors"
                      select="$pnAncestors"/>
      <xsl:with-param name="pnPreceding"
                      select="$pnPreceding+1"/>

</xsl:apply-templates>

</xsl:template>

</xsl:stylesheet>

This transformation is not long, it can be written almost mechanically, it
makes exactly one pass over the tree and it has a linear time complexity
(checked with inputs of different size).

Cheers,

Dimitre Novatchev
FXSL developer,

http://fxsl.sourceforge.net/ -- the home of FXSL
Resume: http://fxsl.sf.net/DNovatchev/Resume/Res.html

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