Re: [xsl] Re: Re: Node Selection

Subject: Re: [xsl] Re: Re: Node Selection
From: Dimitre Novatchev <dnovatchev@xxxxxxxxx>
Date: Fri, 15 Jun 2001 12:13:41 -0700 (PDT)
Hi Jeni,
Moving from O(N*Log2(N)) to just O(N)is a great step forward.

Now I understand that you didn't offer this solution, because someone had just said
he "i felt afraid, when i saw jeni's example"... 

So, the next step will make your solution also look quite simple -- and you know
what this step is -- stop writing customised max() templates on every occasion and
use just one generic max() template. I'm just quoting one of your messages, with
small adjustments:

<date-timeMax:max />

<xsl:template match="/">
  <xsl:text>Maximum value is: </xsl:text>
  <xsl:apply-templates select="document('')/*/date-timeMax:max)" >
    <xsl:with-param name="nodeset" select="//Activity"/>

<xsl:template match="date-timeMax:max">
   <xsl:param name="nodes" select="/.."/>
   <xsl:param name="n1" select="/.."/>
   <xsl:param name="n2" select="/.."/>
   <xsl:value-of select="concat($n1/Date, $n1/Time) 
                         concat($n1/Date, $n1/Time) " />

Dimitre Novatchev.

--- Jeni Tennison <mail@xxxxxxxxxxxxxxxx> wrote:
> Dimitre Novatchev wrote:
> >> > I am using Xalan for xsl transformations. I have some xml with
> >> > multiple <Activity> nodes in it for each part that is processed. The
> >> > activity nodes are not sorted in any way in the xml. I want to
> >> > select only the latest activity (by Date, Time) to process in the
> >> > transform for my output to show the last activity scan on this part
> >> > and ignore all other activity scans.
> >> 
> >> The easiest way to do this is to sort the Activity elements by their
> >> Date and Time (in descending order), and then choose the first one
> >> only to go on and process:
> [snip]
> >
> > This is one of the most inefficient ways to find a maximum and Jeni
> > must know it. In case there are thousands of nodes to be sorted, the
> > unnecessary wait will be due exactly to following such an advice.
> Well I did say *easiest* rather than *most efficient* ;)
> Jim, if you have lots of Activity elements and find that your
> transformation is unacceptably slow, then you could alternatively
> use a recursive template.  This finds the next following Activity that
> occurs after this one, and if there is one then applies templates to
> it in 'latest' mode, and so on recursively through the Activity
> elements.  If there isn't one, it applies templates to the Activity so
> you can go on and process it.
> <xsl:template match="Activity" mode="latest">
>    <xsl:variable name="date-time" select="concat(Date, Time)" />
>    <xsl:variable name="next"
>                  select="following-sibling::Activity
>                             [concat(Date, Time) > $date-time][1]" />
>    <xsl:choose>
>       <xsl:when test="$next">
>          <xsl:apply-templates select="$next" mode="latest" />
>       </xsl:when>
>       <xsl:otherwise>
>          <xsl:apply-templates select="." />
>       </xsl:otherwise>
>    </xsl:choose>
> </xsl:template>
> To kick this process off, you need to apply templates to the first
> Activity element in your Part, in 'latest' mode:
> <xsl:template match="Part">
>    <xsl:apply-templates select="Activity[1]" mode="latest" />
> </xsl:template>
> [Caveat: this template will involve very deep recursion, which might
> still be a problem on some processors (including Xalan, I believe), if
> you're unlucky with the ordering of your Activity elements. It also
> assumes that processors are smart enough to optimise XPath expressions
> that end in a [1] predicate, and to therefore stop when they find the
> first node in the path, but that shouldn't be a problem in Xalan.]
> Cheers,
> Jeni
> ---
> Jeni Tennison

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