Re: [xsl] An XPath expression that avoids writing special case code?

["Wendell Piez wapiez@xxxxxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Roger,

Okay, so the requirement is that if Data[2] is present, it must correspond
with the second argument. It may not be the same (if it is not there at
all) but it must not be different.

<xsl:function name="f:getRow">
    <xsl:param name="element"/>
    <xsl:param name="parent"/>
    <xsl:sequence select="$document/Row[Cell[1]/Data eq
$element][not(Cell[2]/Data ne $parent)]" />
</xsl:function>

(Untested.)

Does this reflect the intent?

Cheers, Wendell


On Fri, Jun 18, 2021 at 8:58 AM Roger L Costello costello@xxxxxxxxx <
xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:

> Hi Wendell,
>
> My XML document may have an element named navaid with a parent element
> named airport and it may have an element named navaid with a parent element
> named enrouteAirway, like this:
>
> <Document>
>     ...
>     <Row>
>         <Cell>
>             <Data>navaid</Data>
>         </Cell>
>         <Cell>
>             <Data>airport</Data>
>         </Cell>
>     </Row>
>     ...
>     <Row>
>         <Cell>
>             <Data>navaid</Data>
>         </Cell>
>         <Cell>
>             <Data>enrouteAirway</Data>
>         </Cell>
>     </Row>
>     ...
> </Document>
>
> To identify that I want the navaid within airport (not the navaid within
> enrouteAirway) I need to specify in the function call both element and
> parent, e.g.,
>
> f:getRow('navaid', 'airport')
>
> Does that make sense?
>
> /Roger
>
> From: Wendell Piez wapiez@xxxxxxxxxxxxxxx <
> xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
> Sent: Friday, June 18, 2021 8:45 AM
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: [EXT] Re: [xsl] An XPath expression that avoids writing special
> casecode?
>
> Roger,
>
> I am fairly puzzled, not by the problem as posed, but whether it is really
> the problem.
>
> Surely, if you had
>
> <xsl:function name="f:getRow">
>     <xsl:param name="element"/>
>     <xsl:sequence select="$document/Row[Cell[1]/Data eq $element]" />
> </xsl:function>
>
> you could call
>
> <xsl:sequence select="f:getRow('airport')" />
>
> and not worry whether a parent is given or not.
>
> Mind you, I also agree with Mike Kay. I think this is a case where since
> your syntax does not clearly reflect the semantics you wish to induce over
> the data, everything becomes harder.
>
> So what's the real question here? My guess is it has to do with what a
> "parent" is and why you want to look at it sometimes, but not other times.
>
> Cheers, Wendell
>
>
> On Thu, Jun 17, 2021 at 10:06 AM Roger L Costello mailto:
> costello@xxxxxxxxx <mailto:xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> Hi Folks,
>
> My XML document contains a bunch of <Row> elements, like so:
>
> <Document>
>     ...
>     <Row>
>         <Cell>
>             <Data>airport</Data>
>         </Cell>
>         <Cell>
>             <Data>airports</Data>
>         </Cell>
>     </Row>
>     ...
> </Document>
>
> I want to fetch the Row whose Cell[1]/Data is 'airport' and whose
> Cell[2]/Data is 'airports'. So I created this XPath expression:
>
> /Document/Row[Cell[1]/Data eq 'airport'][Cell[2]/Data eq 'airports']
>
> I do this kind of fetching operation often, so I created a function to
> fetch the desired Row:
>
> <xsl:function name="f:getRow">
>     <xsl:param name="element"/>
>     <xsl:param name="parent"/>
>     <xsl:sequence select="$document/Row[Cell[1]/Data eq
> $element][Cell[2]/Data eq $parent]" />
> </xsl:function>
>
> I call the function this way:
>
> <xsl:sequence select="f:getRow('airport', 'airports')" />
>
> Sometimes there is an element that doesn't have a parent. That is,
> sometimes I'd like to fetch a Row in which Cell[2] is empty, like this:
>
>     <Row>
>         <Cell>
>             <Data>aviation</Data>
>         </Cell>
>         <Cell/>
>     </Row>
>
> Then this call to f:getRow fails:
>
> <xsl:sequence select="f:getRow('aviation', '')" />        <!-- Those are
> two apostrophes within the parentheses -->
>
> Clearly I need to modify f:getRow. I could add special case code to test
> $parent to see if it is empty (the '' string) and do one thing, and if it's
> not empty do another thing. But I wonder if there is a more elegant
> solution that doesn't involve special case code? Is there a way to modify
> the XPath expression in f:getRow such that it fetches the correct Row
> regardless of whether $parent is empty or not?
>
> /Roger
>
>
>
>
> --
> ...Wendell Piez... ...wendell -at- nist -dot- gov...
> ...wendellpiez.com... ...pellucidliterature.org... ...pausepress.org...
> ...http://github.com/wendellpiez... ...gitlab.coko.foundation/wendell...
> http://www.mulberrytech.com/xsl/xsl-list
> http://lists.mulberrytech.com/unsub/xsl-list/673357 ()
> 
>
>

-- 
...Wendell Piez... ...wendell -at- nist -dot- gov...
...wendellpiez.com... ...pellucidliterature.org... ...pausepress.org...
...github.com/wendellpiez... ...gitlab.coko.foundation/wendell...