Re: [xsl] select immediately following siblings with constraints?

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

Jim,

At 01:54 PM 2/23/2006, you wrote:
> Thank you very much for the reply.  I actually hadn't been aware of
> the << and >> operators, I shall have to read up on them.

Yes, they're fun, and ought to be useful for all kinds of neat things 
we haven't discovered yet.

>   I did think
> about using a for loop, I just wasn't sure how I could write one which
> would be efficent, which wouldn't end up taking a lot more time than
> necessary to run down the remaining following-sibling elements.

Note my attempt with the "for" expression (which actually isn't a 
loop but a mapping operation over a sequence, here applied to fake a 
"let" rather than perform a mapping :-) won't catch following sibling 
a elements when there is no following sibling b, so you'd have to add 
such following sibling a elements explicitly, for completeness.

Thus:

((for $b in following-sibling::b[1]
    return following-sibling::a[. &lt;&lt; $b]),
 (following-sibling::a[not(current()/following-sibling::b)]))

... which is even less orthodox than ever.

Without the current() function you have to do

((for $b in following-sibling::b[1]
    return following-sibling::a[. &lt;&lt; $b]),
 (for $s in .
    return following-sibling::a[not($s/following-sibling::b)]))

I just tried this; amazingly enough it seems to work.

It remains a good question how much of this work should be done in 
XPath. I think the XSLT side is often easier to work with even if 
it's more verbose.

As for efficiency, being blissfully ignorant of most of what happens 
under the covers, I generally don't worry too much about that; but I 
doubt this would be a problem in most documents. (It might be in one 
that was unusually long and flat.) My general attitude is that 
performance is never a problem until it actually is one.

Which of the XPath or XSLT approaches would create more of an 
impression of wizardry, I leave for you to consider. :->

Cheers,
Wendell



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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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