You're using "=" rather than "is" to compare books. That's a dangerous mistake
to make (a) because it gives you the right answer 99% of the time, and (b)
because it's incredibly expensive.

I couldn't think of a better approach with XPath 2.0. As Martin says, it's the
wrong tool for the job.

Michael Kay
Saxonica

> On 2 May 2019, at 13:55, Costello, Roger L. costello@xxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello XPath experts!
>
> At the bottom of this message is my XML document. I need an XPath 2.0
expression that returns the result of this query:
>
> 	Are there any book titles with more than
> 	one binding? If yes, then show the first book
> 	for each binding.
>
> For the below XML document, the query should return these two books:
>
> <Book>
>    <Author>Sally Smith</Author>
>    <Title>XYZ</Title>
>    <Binding>hardcover</Binding>
>    <Count>1</Count>
>    <Description>lo lo lo ..</Description>
> </Book>
> <Book>
>    <Author>Sally Smith</Author>
>    <Title>XYZ</Title>
>    <Binding>softcover</Binding>
>    <Count>1</Count>
>    <Description>do do do ..</Description>
> </Book>
>
> Notice that the two books have the same author and title but different
binding (hardcover versus softcover).
>
> This XPath 2.0 expression seems to work:
>
> for $i in /Bookstore/BookTitle/Book[1],
>    $j in /Bookstore/BookTitle/Book[1] return
>        if (($i ne $j)
>            and ($i/Author eq $j/Author)
>            and ($i/Title eq $j/Title)
>            and ($i/Binding ne $j/Binding)
>            and ($i = $j/preceding::Book))
>        then ($i, $j)
>        else ()
>
> That expression seems awfully complicated. Is there a simpler expression? If
there isn't a simpler expression, then do you see anything missing in the
expression (i.e., something that the expression doesn't take into
consideration)?  /Roger
>
> <Bookstore>
>    <BookTitle>
>        <Book>
>            <Author>John Doe</Author>
>            <Title>ABC</Title>
>            <Binding>hardcover</Binding>
>            <Count>1</Count>
>            <Description>da da da ..</Description>
>        </Book>
>        <Book>
>            <Author>John Doe</Author>
>            <Title>ABC</Title>
>            <Binding>hardcover</Binding>
>            <Count>2</Count>
>            <Description>za za za ..</Description>
>        </Book>
>    </BookTitle>
>    <BookTitle>
>        <Book>
>            <Author>John Doe</Author>
>            <Title>Foo</Title>
>            <Binding>softcover</Binding>
>            <Count>1</Count>
>            <Description>na na na ..</Description>
>        </Book>
>    </BookTitle>
>    <BookTitle>
>        <Book>
>            <Author>Sally Smith</Author>
>            <Title>XYZ</Title>
>            <Binding>hardcover</Binding>
>            <Count>1</Count>
>            <Description>lo lo lo ..</Description>
>        </Book>
>        <Book>
>            <Author>Sally Smith</Author>
>            <Title>XYZ</Title>
>            <Binding>hardcover</Binding>
>            <Count>2</Count>
>            <Description>ho ho ho ..</Description>
>        </Book>
>    </BookTitle>
>    <BookTitle>
>        <Book>
>            <Author>Sally Smith</Author>
>            <Title>XYZ</Title>
>            <Binding>softcover</Binding>
>            <Count>1</Count>
>            <Description>do do do ..</Description>
>        </Book>
>    </BookTitle>
> </Bookstore>