On Tue, Dec 28, 2021 at 4:10 PM Michael Kay mike(_at_)saxonica(_dot_)com <
xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
On 28 Dec 2021, at 23:54, Dimitre Novatchev dnovatchev(_at_)gmail(_dot_)com
<
xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
$nodes[index-of($nodes ! generate-id(.), generate-id(.))[1]]
This seems a candidate for "the shortest solution" and it shouldn't be
inefficient, given a good optimizer:
It probably also gets a prize for the first practical use case of a filter
expression where the predicate is numeric and has different values for
different nodes in the input sequence.
It's going to be O(n*m) unless index-of() is optimized to use some kind of
index or hash lookup rather than a sequential search. That's assuming that
the expression $nodes ! generate-id(.) gets loop-lifted; if it isn't, then
it becomes O(n*n*m).
Seems BaseX is good enough to do this. I increased the number of nodes in
$nodes 3 times and there was no increase in the evaluation time.
Aesthetically, I find generate-id() ugly and it would be nice to avoid it.
Its name is ugly, yes. A shorter and more meaningful name, like id() or
key() would be much better. Maybe we need a mechanism in XPath 4.0 to
specify global aliases (like a using file... )
Cheers,
Dimitre
Michael Kay
Saxonica
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Cheers,
Dimitre Novatchev
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