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Re: [xsl] Best Way to Select Following Elements With An Ancestor?


Subject: Re: [xsl] Best Way to Select Following Elements With An Ancestor?
From: Eliot Kimber <ekimber@xxxxxxxxxxxx>
Date: Sat, 22 Mar 2014 13:00:41 -0500

For my specific problem I only need to know if the nodes exist.

I broke the code into parts mostly to allow me to better understand the
parts.

But I can imagine use cases where I would also want to process the
elements that meet the test.

Cheers,

E.
bbbbb
Eliot Kimber, Owner
Contrext, LLC
http://contrext.com




On 3/22/14, 12:44 PM, "Michael Kay" <mike@xxxxxxxxxxxx> wrote:

>
>On 22 Mar 2014, at 17:16, David Rudel <fwqhgads@xxxxxxxxx> wrote:
>
>> On Sat, Mar 22, 2014 at 1:46 PM, Eliot Kimber <ekimber@xxxxxxxxxxxx>
>>wrote:
>>> I have a document where each child of the root element establishes a
>>> unique content with regard to the output result (in this case,
>>> corresponding to InDesign frames).
>>>
>>> For a given descendant of one of these elements I need to know if there
>>> are any following elements within the same context.
>
>Yes, that's what Eliot wrote, though his code snippet suggested he was
>interested not only in knowing whether or not such a node exists, but
>also in grabbing it.
>
>However, even if you want the next following node that is a descendant of
>D, as some of us assumed, your approach appears useful.
>
>I believe it is true (though I have great trouble proving such things
>rigorously) that $A/following::* is equivalent to
>$A/ancestor-or-self::*/following-sibling::*/descendant-or-self::*.
>
>It then follows that $A/following::*[ancestor::* intersect $D] can be
>rewritten as $A/ancestor-or-self::*[ancestor::* intersect
>$D]/following-sibling::*/descendant-or-self::*, since if $X has $D as an
>ancestor, then every node in
>$X/following-sibling::*/descendant-or-self::* also has $D as an ancestor.
>
>Michael Kay
>
>>
>> I may be thinking about this the wrong way, but it seems like the
>> situation you describe (some following element exists that is a
>> descendant of the same context-setting node) is equivalent to saying
>> "Either this node has a following-sibling, or some ancestor of it has
>> a following-sibling, not counting the context-setting nodes."
>>
>> Is the above accurate?
>>
>> If the above understanding is correct, then a more elegant answer
>> would be to use recursive functions:
>>
>> Define a recursive function that uses the following logic:
>> f($x) = false if $x is one of the context nodes (/child::element())
>> f($x) = true if $x has any following::sibling elements.
>> f($x) = f($x/..) if neither of the above statements resolves the answer.
>>
>> Or, without recursive functions:
>>
>> Define a variable containing the context-setting nodes:
>> $context_nodes = /child::element()
>>
>> Then the predicate you want is:
>>
>>
>>boolean(ancestor-or-self::element()[not($context_nodes)]/following-siblin
>>g::element()
>>
>> -David
>>
>> --
>>
>> "A false conclusion, once arrived at and widely accepted is not
>> dislodged easily, and the less it is understood, the more tenaciously
>> it is held." - Cantor's Law of Preservation of Ignorance.


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