Re: [xsl] [XSLT 1.0] How to get the last number in a string of numbers?

["G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>]

At 2009-12-23 09:01 -0500, Costello, Roger L. wrote:
> I have a variable that contains a bunch of numbers:
>
>    <xsl:variable name="numbers">
>       generate some numbers
>    </xsl:variable>
>
> I want to obtain the last number in $numbers.
>
> For example, this might be the value of $numbers:
>
>    6 23 45 67
>
> I want the last number:
>
>    67
>
> I want the last number fast, i.e., I want it in constant time, not 
> O(n), where n is the length of the list of numbers.
>
> Plus, I don't want to use any extension functions/elements.
>
> Finally, I want to use only XSLT 1.0
>
> Can it be done? How?

I can't think of a way of doing it in constant time because of the 
limited set of functions available.

Is this a real-world problem or just a puzzle?

You don't say why you have the constraint of O(n), which is typical 
when using the design pattern of car/cdr but if you want to reduce 
the number of recursive calls to the length of the last number, I 
thought of a lexical approach below.

I would suppose the advantage with the lexical approach is that the 
string functions are being evaluated behind the scenes and the number 
of executed stylesheet loops (which would be relatively slower) is 
always going to be the length of the last number regardless of 
whether you have one number or a thousand numbers.

In both cases, though, remember that tail recursion optimization 
(implemented in Saxon) is going to make execution really quite quick 
and without occupying any stack space if that was your concern.

Both approaches are illustrated below.

I hope this helps.

. . . . . . . . . . . . Ken

T:\ftemp>xslt roger.xsl roger.xsl

Last: 67
Last: 67
T:\ftemp>type roger.xsl
<?xml version="1.0" encoding="US-ASCII"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
                version="1.0">

<xsl:output method="text"/>

<xsl:variable name="numbers">
    6 23 45 67
</xsl:variable>

<xsl:template match="/">
  <xsl:call-template name="find-last-token-using-tokens">
    <xsl:with-param name="nums" select="normalize-space($numbers)"/>
  </xsl:call-template>

  <xsl:call-template name="find-last-token-using-string">
    <xsl:with-param name="nums" select="normalize-space($numbers)"/>
  </xsl:call-template>
</xsl:template>

<xsl:template name="find-last-token-using-tokens">
  <xsl:param name="nums"/>
  <xsl:choose>
    <xsl:when test="contains($nums,' ')">
      <xsl:call-template name="find-last-token-using-tokens">
        <xsl:with-param name="nums" select="substring-after($nums,' ')"/>
      </xsl:call-template>
    </xsl:when>
    <xsl:otherwise>
Last: <xsl:value-of select="$nums"/>
    </xsl:otherwise>
  </xsl:choose>
</xsl:template>

<xsl:template name="find-last-token-using-string">
  <xsl:param name="nums"/>
  <xsl:param name="last"/>
  <xsl:variable name="last-char"
                select="substring($nums,string-length($nums))"/>
  <xsl:choose>
    <xsl:when test="$last-char and $last-char!=' '">
      <xsl:call-template name="find-last-token-using-string">
        <xsl:with-param name="nums"
                        select="substring($nums,1,string-length($nums)-1)"/>
        <xsl:with-param name="last"
                        select="concat($last-char,$last)"/>
      </xsl:call-template>
    </xsl:when>
    <xsl:otherwise>
Last: <xsl:value-of select="$last"/>
    </xsl:otherwise>
  </xsl:choose>
</xsl:template>

</xsl:stylesheet>

T:\ftemp>

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