Re: [xsl] XPath expression to check that there are no intervening elements?

["G. Ken Holman g.ken.holman@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

I like Mike's answer for XSLT 2.

Your XSLT 1 solution can be improved by reducing the number of 
counting actions.  Your solution has three uses of count() ... this 
has only two:

  count(B[last()]/preceding-sibling::*[not(self::B)]) =
  count(B[1]/preceding-sibling::*[not(self::B)])

Avoiding the use of counting you could do the following:

  string( generate-id( B[1]/preceding-sibling::*[not(self::B)][1] ) ) =
  string( generate-id( B[last()]/preceding-sibling::*[not(self::B)][1] ) )

The use of string() is necessary in case the sequence of children 
starts with B.

Come to think of it, neither your answer, Mike's answer nor my answer 
will work if there are no B children at all.  You will get a false 
positive.  Does your test need to accommodate that situation?

. . . . . . . . Ken

At 2016-07-19 15:44 +0000, Costello, Roger L. costello@xxxxxxxxx wrote:
> Hi Folks,
>
> This XML has a solid block of <B> elements:
>
> <Document>
>     <A/>
>     <B/>
>     <B/>
> </Document>
>
> This XML has an intervening <C> element:
>
> <Document>
>     <A/>
>     <B/>
>     <C/>
>     <B/>
> </Document>
>
> I need an XPath expression to return a Boolean value:
>
>         Return true if there is one solid block of <B> elements
>                 (no intervening elements).
>         Otherwise, return false.
>
> I created a horrendous XPath expression to solve it:
>
> count(B) eq (B[last()]/count(preceding-sibling::*)+1 - 
> B[1]/count(preceding-sibling::*))
>
> Can you provide a better (simpler, more efficient) XPath expression?
>
> /Roger


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