Firstly, I missed this, to select the first member in an array you need
$groups?1 rather than $groups[1].

Secondly, if $rows is a sequence of row elements then $rows/row selects
nothing because a row doesn't have a child::row.

Thirdly, I'm not sure why you expect the 'Foo' row to be in the first group.
distinct-values() loses order.

Michael Kay
Saxonica

> On 6 Jun 2019, at 16:15, Costello, Roger L. costello@xxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hi Michael,
>
> That XPath expression yields the empty set.
>
> I created these variables:
>
> <xsl:variable name="first-group" select="$groups[1]" />
> <xsl:variable name="Foo-row-first-group" select="($first-group?*)/row[Data
eq 'Foo']"/>
>
> And then output the value of the second variable:
>
> <Foo-row-in-first-group>
>    <xsl:sequence select="$Foo-row-first-group" />
> </Foo-row-in-first-group>
>
> This is the output:
>
> <Foo-row-in-first-group/>
>
> Why does the XPath yield the empty set? Clearly the first group contains a
<row> element with a <Data> element with value 'Foo'. Thoughts?
>
> /Roger
>
>
> From: Michael Kay mike@xxxxxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
> Sent: Thursday, June 6, 2019 10:47 AM
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: [EXT] Re:  Each value in an XPath array is a sequence of
elements... how to access a particular element in a particular array value?
>
> $first_group is an array of nodes. To turn it into a sequence of nodes, use
"?*". So it's
>
> ($first_group?*)/row
>
> (parentheses because I don't have the operator precedences in my head)
>
> Michael Kay
> Saxonica
>
>
>
>
> On 6 Jun 2019, at 15:26, Costello, Roger L. mailto:costello@xxxxxxxxx
<mailto:xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hi Folks,
>
> This is an extension to a question that I had last week ...
>
> Recall that I want to group the <row> elements in the following XML. Each
group should consist of those <row> elements that have the same ARPT__IDENT,
TRM__IDENT values.
>
> <Test>
>    <row>
>        <ARPT__IDENT>A</ARPT__IDENT>
>        <TRM__IDENT>X</TRM__IDENT>
>        <Data>Foo</Data>
>    </row>
>    <row>
>        <ARPT__IDENT>A</ARPT__IDENT>
>        <TRM__IDENT>X</TRM__IDENT>
>        <Data>Bar</Data>
>    </row>
>    <row>
>        <ARPT__IDENT>A</ARPT__IDENT>
>        <TRM__IDENT>Y</TRM__IDENT>
>        <Data>Blah</Data>
>    </row>
>    <row>
>        <ARPT__IDENT>A</ARPT__IDENT>
>        <TRM__IDENT>Y</TRM__IDENT>
>        <Data>Plugh</Data>
>    </row>
> </Test>
>
> That XML consists of two groups. Each group has two <row> elements.
>
> Martin provided a great XPath 3.1 expression for doing the grouping:
>
> <xsl:variable name="groups" as="array(element(row))*" select="
>    let $keys :=
>        distinct-values($rows/concat(ARPT__IDENT, '|', TRM__IDENT))
>    return
>        for $i in $keys
>        return
>            array {$rows[$i = concat(ARPT__IDENT, '|', TRM__IDENT)] }
>    "/>
>
> In the following, I select the first group:
>
> <xsl:variable name="first-group" select="$groups[1]" />
>
> Next, I want to select the <row> element in the first group that has Foo as
the value of the <Data> element. I thought that this would be the appropriate
XPath expression:
>
> <xsl:variable name="Foo-row-first-group" select="$first-group/row[Data eq
'Foo']"/>
>
> Apparently it is not the appropriate XPath expression, because I get this
error message:
>
> 	Axis step child::element(Q{}row) cannot
> 	be used here: the context item is not a node
>
> What is the appropriate XPath expression, please?
>
> /Roger
>
> http://www.mulberrytech.com/xsl/xsl-list
> http://lists.mulberrytech.com/unsub/xsl-list/673357 ()