[xsl] Re: Key and/or grouping questions.

["Edward L. Knoll" <ed.knoll@xxxxxxxxxxxxxx>]

"Edward L. Knoll" wrote:
> 
> > > I have a set of style sheets which have a sever performance
> > > problem. Distilled (hopefully not diluted past usefulness), I
> > > am processing a
> > > large set of sibling elements a few elements at a time.   I
> > > believe the
> > > problem is with the following statement (which I've
> > > changed/condensed the expression of):
> > >
> > > <xsl:for-each  select="/elements[ (position() &gt;= $Start) and
> > > (position() &lt;= $End) ]">
> > > ...
> > > </xsl:for-each>
> >
> > I suspect it actually starts "//elements", because you can't have more
> > than one element that's a child of the root node. But the fact that
> > position() works suggests that they are siblings. Without seeing your
> > source, the first step might be to change this to /*/elements[...]. The
> > next step would be to create a global variable whose value is
> > /*/elements, and replace the for-each by
> >
> > select="$var[position() ...]
> >
> > > I was referred to a FAQ on grouping and this led me to
> > > attempt to setup
> > > some kind of solution utilizing keys.   Unfortunately, the
> > > XSL reference
> > > I have has no information on <xsl:key> and my favorite FAQ
> > > has a list of topics under keys with no corresponding
> > > content.  Anyway, my XSL processor (Xalan) doesn't like my
> > > key definition.  Is the "use" parameter limited from being a
> > > numerical expressions?
> > >
> > > <xsl:key name="PageKey" match="/gnsl:Results/gnsl:Table/gnsl:Row"
> > >          use="((position() - 1) / $RowsPerPage) + 1)" />
> > >
> >
> > It helps in any XPath expression to balance the parentheses properly.
> >
> > But your problem here is misunderstanding what "position()" means. It
> > means the position of the context node in the sequence of nodes
> > currently being processed. In <xsl:key> it will always be 1.
> >
> > What you want is something like:
> >
> >    use="count(preceding-sibling::*)"
> >
> > But I suspect this may not help you, because it's likely to be very
> > expensive to build this index.
> >
> > I think a better approach would be to restructure your code to use the
> > usual:
> >
> > <xsl:for-each select="xx[position() mod $size = 1]">
> >   ..
> >   <xsl:for-each select=".|following-sibling[position() &lt;= $size]">
> 
> Trying something similar to the nested for-each, excpet my outer
> for-each is somthing similar to the following:
> 
>    <xsl:for-each select="xx[position() = $startPos]">
> 
> I get the line at the starting postion just fine, but I get none of the
> following-sibling elements.  If the outer loop selects one element (or
> even every nth element), are the elements selected by the outer loop
> going to have siblings other than those selected by the outer loop; I'm
> guessing not.  I suspect the inner loop in the algorithm above is going
> to process a number nodes equal to $size, but those nodes will be every
> nth element from the xx where n = $size.
> 
> If I've missed something, please let me know.

Syntax error again; the following works:

  <xsl:for-each select=".|following-sibling::*[position() &lt;= $size]">

-- 
Edward L. Knoll   Phone (work)     : (719)484-2717
                  e-mail (work)    : ed.knoll@xxxxxxxxxxxxxx
                  e-mail (business): eknoll@xxxxxxxxxx
                  e-mail (personal): edward@xxxxxxxxxxx

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