On 29.12.2021 17:36, Dimitre Novatchev dnovatchev(_at_)gmail(_dot_)com wrote:
On Wed, Dec 29, 2021 at 12:21 AM Martin Honnen
martin(_dot_)honnen(_at_)gmx(_dot_)de
<mailto:martin(_dot_)honnen(_at_)gmx(_dot_)de>
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com
<mailto:xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com>> wrote:
Am 29.12.2021 um 00:32 schrieb Dimitre Novatchev
dnovatchev(_at_)gmail(_dot_)com <mailto:dnovatchev(_at_)gmail(_dot_)com>:
Hit Send too early:
Do notice: this seems the only solution of all presented so far,
that preserves the original sequence order (not document order) of
the nodes.
Why is the original sequence order preserved?
https://www.w3.org/TR/xpath-functions/#func-distinct-values
<https://www.w3.org/TR/xpath-functions/#func-distinct-values>
clearly says
"The function returns the sequence that results from removing
from|$arg|all but one of a set of values that are considered equal
to one another. [...]
The order in which the sequence of values is returned
is·implementation-dependent·
<https://www.w3.org/TR/xpath-functions/#implementation-dependent>.
Which value of a set of values that compare equal is returned
is·implementation-dependent·
<https://www.w3.org/TR/xpath-functions/#implementation-dependent>."
So while
$nodes ! generate-id(.)
gives you the generated ids in the order of the nodes in $nodes
after the call to distinct-values there is no order defined, it is
implementation dependent.
@Martin Honnen <mailto:Martin(_dot_)Honnen(_at_)gmx(_dot_)de> Could you,
please, give us
an example of an existing XPath engine whose implementation of
`distinct-values()` produces its results in any other order than their
original order in the input sequence?
I don't have to know one, I just pointed out that the spec doesn't
guarantee the order. Thus I don't see why, given the spec, one should
expect any implementation to preserve the order.
Imagine you implement distinct-values in .NET with e.g.
https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.distinct?view=net-6.0
and it would probably pass all tests but also only give a "result
sequence" that " is unordered".
Aren't there also implementations of XQuery or XPath that exploit
parallel processing? I could imagine such an implementation to easily
not care about ordering if the spec allows it for distinct-values.
It seems, on the other hand, eXide of eXist-db in the online version
doesn't even grok some of the generate-id based attempts:
let $nodes := (1 to 10) ! parse-xml-fragment('<node>' || . ||
'</node>')/node(),
$nodes := (1 to 5) ! $nodes,
$ids := distinct-values($nodes ! generate-id(.))
return $ids ! (function($id) {$nodes[generate-id(.) eq $id][1]})(.)
gives <node>1</node>
Any eXist-db users reading here? Is there a known issue with generate-id?
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