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RE: [xsl] Collating riffled lists

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Michael

Thanks for the info. I tried it and it works on the abstract problem as
advertised.

And thanks for your XSLT book! It's been a great help to this XSLT newbie.

Unfortunately, the real-life problem is less well-structured than the
abstraction.

Here's another abstraction that better captures the (lack of) structure of
the problem. As before, I believe this runs O(n^2) and n is large. I'd like
to try to stick with XSLT 1.0 if possible. Any improvements are most
welcome. If this is as good as it gets, that would also be useful info.

Here's what I'd like to be able to do: Create a recursive function to build
a node list of all the b's, then select from that with an index. I think
that would need 1.1 or processor-specific extensions, however.

XML source:

<?xml version="1.0"?>
<list>
<item>something else</item>
<item>a a1</item>
<item>a a2</item>
<item>something else</item>
<item>a a3</item>
<item>b b1</item>
<item>something else</item>
<item>b b2</item>
<item>a a4</item>
<item>b b3</item>
<item>a a5</item>
<item>b b4</item>
<item>a a6</item>
<item>b b5</item>
<item>b b6</item>
</list>

A recursive solution:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">

<!-- match first a and make top level call to recursive template -->
<xsl:template match="item[1]">
  <xsl:call-template name="do_a">
    <xsl:with-param name="ix" select="0" />
  </xsl:call-template>
</xsl:template>

<!-- recursive template counts a's -->
<xsl:template name="do_a">
  <xsl:param name="ix" />

  <xsl:choose>
    <xsl:when test="starts-with(., 'a')">
      <!-- Output the a -->
      <xsl:text>&#xA;</xsl:text>
      <xsl:value-of select="$ix + 1" />
      <xsl:text>: </xsl:text>
      <xsl:value-of select="substring-after(.,' ')" />
      <xsl:text> </xsl:text>

      <!-- Output the corresponding b -->
      <xsl:for-each select="//item[1]">
        <xsl:call-template name="do_b">
          <xsl:with-param name="ix" select="$ix + 1" />
        </xsl:call-template>
      </xsl:for-each>

      <!-- process remaining a's -->
      <xsl:for-each select="following::item[1]">
        <xsl:call-template name="do_a">
             <xsl:with-param name="ix" select="$ix + 1" />
        </xsl:call-template>
      </xsl:for-each>
    </xsl:when>
    <xsl:otherwise>
      <!-- Look for next a -->
      <xsl:for-each select="following::item[1]">
        <xsl:call-template name="do_a">
             <xsl:with-param name="ix" select="$ix" />
        </xsl:call-template>
      </xsl:for-each>
    </xsl:otherwise>
  </xsl:choose>
</xsl:template>

<!-- recursive template outputs the ix-th b -->
<xsl:template name="do_b">
  <xsl:param name="ix" />

  <xsl:choose>
    <xsl:when test="starts-with(., 'b')">
      <xsl:choose>
        <xsl:when test="$ix = 1">
          <xsl:value-of select="substring-after(.,' ')" />
        </xsl:when>
        <xsl:otherwise>
          <!-- Look for next b -->
          <xsl:for-each select="following::item[1]">
            <xsl:call-template name="do_b">
                 <xsl:with-param name="ix" select="$ix - 1" />
            </xsl:call-template>
          </xsl:for-each>
        </xsl:otherwise>
      </xsl:choose>
    </xsl:when>
    <xsl:otherwise>
      <!-- Look for next b -->
      <xsl:for-each select="following::item[1]">
        <xsl:call-template name="do_b">
             <xsl:with-param name="ix" select="$ix" />
        </xsl:call-template>
      </xsl:for-each>
    </xsl:otherwise>
  </xsl:choose>
</xsl:template>
<!-- suppress other output -->
<xsl:template match="text()" />

</xsl:stylesheet>

Output:

<?xml version="1.0" encoding="utf-8"?>
1: a1 b1
2: a2 b2
3: a3 b3
4: a4 b4
5: a5 b5
6: a6 b6

Thanks,
                Mat


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