Subject: Re: [xsl] for vs. for-each From: "Dimitre Novatchev dnovatchev@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> Date: Sun, 14 Mar 2021 19:48:32 -0000 |
On Sun, Mar 14, 2021 at 11:55 AM Michael Kay mike@xxxxxxxxxxxx < xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> 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 MC<ller-Hillebrand mmh@xxxxxxxxx < > xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> 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
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