Re: [xsl] applying a predicate to a sorted sequence

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

Kevin,

The easy answer is "yes".

The more complete and correct answer is that you need to distinguish 
between XPath 2.0 and XPath 1.0 here. In 2.0 the result of a sort will be a 
sequence (presumably of nodes), which has an order. Filtering it with a 
predicate should not alter that. (There is a special case if the filtered 
expression is a step along a reverse XPath axis, but this shouldn't apply 
to your case as you're filtering a sequence bound to a variable. Although 
it does seem on reflection that the special case makes the whole thing 
perhaps worth testing in your implementation....)

In XPath 1.0 there is actually no such thing as a sequence; what you have 
is actually a node-set, and as such has no intrinsic order. Accordingly, 
the unordered set $variable, when filtered, gives an unordered set. When it 
needs an order, the usual rule in XSLT 1.0 is to refer to "document order". 
Naturally this would sort the filtered subset into the same order as it 
would sort the set.

Since you refer to xsl:perform-sort, I assume the XPath 2.0 reasoning is 
what applies to your case.

Cheers,
Wendell

At 12:45 PM 4/29/2005, you wrote:
> If I've got a variable bound to the result of xsl:perform-sort and then
> filter it with a predicate (e.g. select="$variable[@attribute='value']"),
> is the order of the resulting sequence guaranteed to be stable with
> respect to the original sorted sequence?
>
> Thanks,
> --
> Kevin Rodgers


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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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