RE: [xsl] Extract First node

Subject: RE: [xsl] Extract First node
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Fri, 02 Sep 2005 16:53:00 -0400
I think what the OP wanted was

<xsl:template match="/a">
  <xsl:value-of select="(b/c[@type='pdf'])[1]" />

as David B. suggested.

I believe the difference between 1.0 and 2.0 value-of is a red herring here, as the XPath was simply not correct.

The difference is between


which is short for child::b/child::c[attribute::type='pdf'][1]



which is short for (child::b/child::c[attribute::type='pdf'])[1]

The first expression selects all such c grandchildren that are the first such children of their b parents (there were several in the sample given); the second selects only the first such c grandchildren of the entire set of such c grandchildren.

At 02:14 PM 9/2/2005, Mike wrote:
 <xsl:value-of select="b[c[@type='pdf']][1]/c/text()"/>

Can you explain how b[c[@type='pdf']]work?  I'm not familiar with that.
Is it v2.0 syntax?

It's perfectly fine 1.0 syntax, just not useful here. It's short for


and basically just filters the b children here to those that have such a c child.

The logic of predicates (the [ ] syntax) is simple: test the expression given for each node in the node set to which it applies; cast the result, if necessary, to a Boolean value (this happens implicitly). Keep any node for which the expression is true; toss any for which it is false.

Inside a predicate, "child::c" tests true for context nodes that have a c element child; "c[@type='pdf']" tests true for context nodes that have a c element child that have a type attribute = 'pdf', etc.


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