XPath "following siblings before"

Question

Hi,

I'm trying to select elements (a) with XPath 1.0 (or possibly could be with Regex) that are following siblings of particular element (b) but only preceed another b element.

<img><b>First</b><br>&nbsp;&nbsp;
<img>&nbsp;&nbsp;<a href="/first-href">First Href</a> - 19:30<br>
<img><b>Second</b><br>&nbsp;&nbsp;
<img>&nbsp;&nbsp;<a href="/second-href">Second Href</a> - 19:30<br>
<img>&nbsp;&nbsp;<a href="/third-href">Third Href</a> - 19:30<br>

I tried to make the sample as close to real world as possible. So in this scenario when I'm at element

<b>First</b>

I need to select

<a href="/first-href">First Href</a> 

and when I'm at

<b>Second</b> 

I need to select

<a href="/second-href">Second Href</a> 
<a href="/third-href">Third Href</a>

Any idea how to achieve that? Thank you!

Answer 1

Dynamically create this XPath:

following-sibling::a[preceding-sibling::b[1][.='xxxx']]

where 'xxxx' is the replaced with the text of the current <b>.

This is assuming that all the elements actually are siblings. If they are not, you can try to work with the preceding and following axes, or you write a more specific XPath that better resembles document structure.

In XSLT you could also use:

following-sibling::a[
  generate-id(preceding-sibling::b[1]) = generate-id(current())
]

Answer 2

Here is a solution which is just a single XPath expression.

Using the Kaysian formula for intersection of two nodesets $ns1 and $ns2:

  $ns1[count(. | $ns2) = count($ns2)]

We simply substitute $ns1 with the nodeset of <a> siblings that follow the current <b> node, and we substitute $ns2 with the nodeset of <a> siblings that precede the next <b> node.

Here is a complete transformation that uses this:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"&gt;
 <xsl:output omit-xml-declaration="yes" indent="yes"/>

  <xsl:template match="/">
   <xsl:apply-templates select="*/b"/>
  </xsl:template>

  <xsl:template match="b">
    At: <xsl:value-of select="."/>

    <xsl:variable name="vNextB" select="following-sibling::b[1]"/>

    <xsl:variable name="vA-sAfterCurrentB" select="following-sibling::a"/>

    <xsl:variable name="vA-sBeforeNextB" select=
    "$vNextB/preceding-sibling::a
    |
     $vA-sAfterCurrentB[not($vNextB)]
    "/>

    <xsl:copy-of select=
     "$vA-sAfterCurrentB
              [count(.| $vA-sBeforeNextB)
              =
               count($vA-sBeforeNextB)
               ]
    "/>
  </xsl:template>
</xsl:stylesheet>

When this transformation is applied on the following XML document:

<t>
    <img/>
    <b>First</b>
    <br />&#xA0;&#xA0;
    <img/>&#xA0;&#xA0;
    <a href="/first-href">First Href</a> - 19:30
    <br />
    <img/>
    <b>Second</b>
    <br />
    <img/>&#xA0;&#xA0;
    <a href="/second-href">Second Href</a> - 19:30
    <br />
    <img/>&#xA0;
    <a href="/third-href">Third Href</a> - 19:30
    <br />
</t>

the correct result is produced:

   At: First <a href="/first-href">First Href</a>
    At: Second <a href="/second-href">Second Href</a>
<a href="/third-href">Third Href</a>