XPath to return all ANCESTORS until - xslt

Question

This is a variant on the common request for an XPath to return all siblings until some condition, answered with characteristic fullness by Dimitre Novatchev at XPath axis, get all following nodes until using this pattern:
$x/following-sibling::p
[1 = count(preceding-sibling::node()[name() = name($x)][1] | $x)]
But that pattern relies on the symmetry of following-sibling and preceding-sibling, on the ability to look in both directions along an axis.
Is there a comparable pattern when the axis is ancestor-or-self?
For example:
<t>
<a xml:base="/news/" >
<b xml:base="reports/">
<c xml:base="politics/" />
<c xml:base="sports/" >
<d xml:base="reports/" />
<d xml:base="photos/" >
<img url="A1.jpg" />
<img url="A2.jpg" />
</d>
</c>
<c xml:base="entertainment" />
</b>
</a>
</t>
The straighforward
<xsl:template match="img">
<xsl:for-each select="ancestor-or-self::*[#xml:base]">
<xsl:value-of select="#xml:base"/>
</xsl:for-each>
<xsl:value-of select="#url"/>
</xsl:template>
would return
/news/reports/sports/photos/A1.jpg
/news/reports/sports/photos/A1.jpg
but if
<c xml:base="sports/" >
were instead
<c xml:base="/sports/" >
with that leading /, the for-each needs to stop, so as to return
/sports/photos/A1.jpg
/sports/photos/A2.jpg
How (in XSLT/XPath 1.0) to make it stop?

Answer 1

This XSLT 1.0 transformation:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:param name="pWanted" select="//img"/>
<xsl:param name="pWantedAttr" select="'url'"/>
<xsl:template match="/">
<xsl:apply-templates select="$pWanted"/>
</xsl:template>
<xsl:template match="*[not(starts-with(#xml:base, '/'))]">
<xsl:apply-templates select="ancestor::*[#xml:base][1]"/>
<xsl:value-of select="concat(#xml:base,#*[name()=$pWantedAttr])"/>
<xsl:if test="not(#xml:base)"><xsl:text>
</xsl:text></xsl:if>
</xsl:template>
<xsl:template match="*[starts-with(#xml:base, '/')]">
<xsl:value-of select="#xml:base"/>
</xsl:template>
</xsl:stylesheet>
when applied to this XML document:
<t>
<a xml:base="/news/" >
<b xml:base="reports/">
<c xml:base="politics/" />
<c xml:base="/sports/" >
<d xml:base="reports/" />
<d xml:base="photos/" >
<img url="A1.jpg" />
<img url="A2.jpg" />
</d>
</c>
<c xml:base="entertainment" />
</b>
</a>
</t>
produces the wanted, correct result:
/sports/photos/A1.jpg
/sports/photos/A2.jpg
Update -- A single XPath 2.0 expression solution:
for $target in //img,
$top in $target/ancestor::*[starts-with(#xml:base,'/')][1]
return
string-join(
(
$top/#xml:base
, $top/descendant::*
[#xml:base and . intersect $target/ancestor::*]
/#xml:base
, $target/#url,
'
'
),
''
)
XSLT 2.0 - based verification:
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="/">
<xsl:sequence select=
"for $target in //img,
$top in $target/ancestor::*[starts-with(#xml:base,'/')][1]
return
string-join(
(
$top/#xml:base
, $top/descendant::*
[#xml:base and . intersect $target/ancestor::*]
/#xml:base
, $target/#url,
'
'
),
''
)
"/>
</xsl:template>
</xsl:stylesheet>
When this transformation is applied on the provided XML document:
<t>
<a xml:base="/news/" >
<b xml:base="reports/">
<c xml:base="politics/" />
<c xml:base="sports/" >
<d xml:base="reports/" />
<d xml:base="photos/" >
<img url="A1.jpg" />
<img url="A2.jpg" />
</d>
</c>
<c xml:base="entertainment" />
</b>
</a>
</t>
the XPath expression is evaluated and the result from this evaluation is copied to the output:
/news/reports/sports/photos/A1.jpg
/news/reports/sports/photos/A2.jpg
With the modified document:
<t>
<a xml:base="/news/" >
<b xml:base="reports/">
<c xml:base="politics/" />
<c xml:base="/sports/" >
<d xml:base="reports/" />
<d xml:base="photos/" >
<img url="A1.jpg" />
<img url="A2.jpg" />
</d>
</c>
<c xml:base="entertainment" />
</b>
</a>
</t>
again the wanted, correct result is produced:
/sports/photos/A1.jpg
/sports/photos/A2.jpg
Update2:
The OP has suggested this simplification:
Update added by original poster: Once embedded in the full
application, where the full url replaced the relative one, Dimitre's
approach ended up being this simple
:
<xsl:template match="#url">
<xsl:attribute name="url">
<xsl:apply-templates mode="uri" select=".." />
<xsl:value-of select="."/>
</xsl:attribute>
</xsl:template>
<xsl:template match="*" mode="uri">
<xsl:if test="not(starts-with(#xml:base, '/'))">
<xsl:apply-templates select="ancestor::*[#xml:base][1]" mode="uri"/>
</xsl:if>
<xsl:value-of select="#xml:base"/>
</xsl:template>

Answer 2

There is a way to select the right nodes in a single for-each select expression:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="img">
<xsl:for-each select="
ancestor-or-self::*[
starts-with(#xml:base, '/')
][1]/descendant-or-self::*[
#xml:base and .//img[generate-id() = generate-id(current())]
]">
<xsl:value-of select="#xml:base"/>
</xsl:for-each>
<xsl:value-of select="#url"/>
</xsl:template>
</xsl:stylesheet>
Given this input XML:
<t>
<a xml:base="/news/" >
<b xml:base="reports/">
<c xml:base="politics/" />
<c xml:base="/sports/" >
<d xml:base="reports/" />
<d xml:base="photos/" >
<img url="A1.jpg" />
<img url="A2.jpg" />
</d>
</c>
<c xml:base="entertainment" />
</b>
</a>
</t>
The correct result is produced:
/sports/photos/A1.jpg
/sports/photos/A2.jpg
The XPath expression could be read as "Beginning with the closest ancestor whose #xml:base starts with a slash, select that and all of its descendants who have the current <img> as one of their descendants."
This effectively selects exactly the one correct path down into the XML tree.

Answer 3

I found it: Count the ancestors that meet the condition before going into the for-each loop. Test each candidate to see if the count of its condition-matching ancestors is the same.
This stylesheet
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
<xsl:template match="img">
<xsl:variable name="distance" select="count(ancestor-or-self::*[#xml:base][substring(#xml:base,1,1)='/'])" />
<xsl:for-each select="ancestor-or-self::*[#xml:base][
count(ancestor-or-self::*[#xml:base][substring(#xml:base,1,1)='/'])=$distance
]">
<xsl:value-of select="#xml:base"/>
</xsl:for-each>
<xsl:value-of select="#url"/>
</xsl:template>
</xsl:stylesheet>
applied to the given XML
<t>
<a xml:base="/news/" >
<b xml:base="reports/">
<c xml:base="politics/" />
<c xml:base="/sports/" >
<d xml:base="reports/" />
<d xml:base="photos/" >
<img url="A1.jpg" />
<img url="A2.jpg" />
</d>
</c>
<c xml:base="entertainment" />
</b>
</a>
</t>
returns the desired result:
/sports/photos/A1.jpg
/sports/photos/A2.jpg
Without the / before sports, the for-each matches ancestors all the way to /news:
/news/reports/sports/photos/A1.jpg
/news/reports/sports/photos/A2.jpg

Answer 4

With a minor change to your original template:
<xsl:template match="img">
<xsl:for-each select="ancestor-or-self::*[#xml:base][not(.//*[starts-with(#xml:base, '/')])]">
<xsl:value-of select="#xml:base"/>
</xsl:for-each>
<xsl:value-of select="#url"/>
</xsl:template>