Finally a good progress has been made on one of the proposals for XPath 4:
Retrieving a sequence of items from a given sequence based on a sequence of
indexes
(https://github.com/qt4cg/qtspecs/issues/50)
With this proposal:
https://github.com/qt4cg/qtspecs/issues/50#issuecomment-799228627 ,
Michael Kay defines a concrete operator syntax and explores and evolves the
main idea to its logical boundaries.
I find the result to match exactly what I had wished for.
Thank you, Dr. Kay!
On Sun, Mar 14, 2021 at 12:48 PM Dimitre Novatchev
<dnovatchev(_at_)gmail(_dot_)com>
wrote:
On Sun, Mar 14, 2021 at 11:55 AM Michael Kay mike(_at_)saxonica(_dot_)com <
xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
For 4.0, however, I would like to see better ways of accessing items in
a sequence by position, and there has been much discussion about how best
to achiieve this.
Yes, we already do have the index-of() function, but we need a reverse to
this:
from-indexes($vSeq, $vIndexes)
and this would produce a sequence with items each of which is the item of
$vSeq at position the value of the $index-value in $vIndexes, when
$index-value iterates over $vIndexes, ot more strictly:
for $ind in $vIndexes
return $vSeq[$ind]
Why reverse of index-of() ?
Because, for any $x in $vSeq it is true that
from-indexes($vSeq, index-of($vSeq, $x))
is a sequence containing all $x items from $vSeq.
Or:
$x eq distinct-values( from-indexes($vSeq, index-of($vSeq, $x)) )
Or if we had sets in XPath, then:
set {$x} === set { from-indexes($vSeq, index-of($vSeq, $x)) }
And this can also be written as:
set {$x} === set { $vSeq => from-indexes( $vSeq => index-of($x)) }
There is even this proposal for an operator notation for the
from-indexes() function, but individual preferences at present seem to vary
too much in order to choose such an operator:
https://github.com/qt4cg/qtspecs/issues/50
Thanks,
Dimitre
Michael Kay
Saxonica
On 14 Mar 2021, at 18:04, Michael Müller-Hillebrand
mmh(_at_)docufy(_dot_)de <
xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
Folks,
Given a variable with a sequence of values
<xsl:variable name="values" select="(1,2,3,4,5)" as="xs:double+"/>
these are three methods to report its content
<xsl:sequence select="for $i in 1 to count($values) return
$values[$i]"/>
<xsl:for-each select="1 to count($values)">
<xsl:sequence select="$values[.]"/>
</xsl:for-each>
<xsl:for-each select="1 to count($values)">
<xsl:sequence select="$values[current()]"/>
</xsl:for-each>
The first works as expected, the second does not, but the third
astonishingly enough gives me the same result as the first. Check it out:
https://xsltfiddle.liberty-development.net/ei5R4v8/2
I read/understand that there is a difference between a for expression
and a path expression, but since we can use atomized values in
xsl:for-each, I would like to see more similarity between for and for-each.
Should this be on the wishlist for XSLT 4 or do I have to
learn/understand some more concepts?
Puzzled greeting,
- Michael
--
Cheers,
Dimitre Novatchev
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