XSLT - Identify consecutive nodes which has same patterns of attribute values

Question

I have xml like this,

<section>
        <p id="ss_main">aa</p>
        <p id="ss_chap">bb</p>
        <p id="main">cc</p>
        <p id="main">dd</p>
        <p id="main">ee</p>
        <p id="ss_main">ff</p>
        <p id="main">gg</p>
        <p id="main">hh</p>
        <p id="main">ii</p>
        <p id="main">jj</p>
        <p id="ss_chap">xx</p>
        <p id="ss_main">yy</p>
        <p id="ss_chap">zz</p>
    </section>

what my requirement is place new nodes named <ss_start> and <ss_end> by covering existing nodes witch are start with ss.

so the output should be,

<section>
        <ss_start/>
        <p id="ss_main">aa</p>
        <p id="ss_chap">bb</p>
        <ss_end/>
        <p id="main">cc</p>
        <p id="main">dd</p>
        <p id="main">ee</p>
        <ss_start/>
        <p id="ss_main">ff</p>
        <ss_end/>
        <p id="main">gg</p>
        <p id="main">hh</p>
        <p id="main">ii</p>
        <p id="main">jj</p>
        <ss_start/>
        <p id="ss_chap">xx</p>
        <p id="ss_main">yy</p>
        <p id="ss_chap">zz</p>
        <ss_end/>
    </section>

I can write xsl like follows to cover specific node by <ss_start> and <ss_end>

<xsl:template match="p[@id='ss_main']">
        <ss_start/>
        <p id="ss_main"><xsl:apply-templates/></p>
        <ss_end/>
    </xsl:template>

but I'm struggling to find consecutive nodes that id attr starting from ss and cover them by <ss_start> and <ss_end>.

Can anyone suggest me a method how can I do this?

Answer 1

XSLT 1.0 sibling recursion

In XSLT 1.0 you can do this as follows, which uses a technique called sibling recursion (though sibling traversal is probably a better term).

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    version="1.0">

    <xsl:output indent="yes" />

    <xsl:template match="node() | @*">
        <xsl:copy>
            <xsl:apply-templates select="node() | @*" />
        </xsl:copy>
    </xsl:template>

    <xsl:template match="section">
        <xsl:copy>
            <xsl:apply-templates select="*[1]" />
        </xsl:copy>
    </xsl:template>

    <xsl:template match="section/*[starts-with(@id, 'ss')]" priority="5">
        <xsl:if test="self::*[not(preceding-sibling::*[1][starts-with(@id, 'ss')])]">
            <ss_start />
        </xsl:if>
        <xsl:copy>
            <xsl:apply-templates select="node() | @*" />
        </xsl:copy>
        <xsl:if test="self::*[not(following-sibling::*[1][starts-with(@id, 'ss')])]">
            <ss_end />
        </xsl:if>
        <xsl:apply-templates select="following-sibling::*[1]" />
    </xsl:template>

    <xsl:template match="section/*">
        <xsl:copy>
            <xsl:apply-templates select="node() | @*" />
        </xsl:copy>
        <xsl:apply-templates select="following-sibling::*[1]" />
    </xsl:template>

</xsl:stylesheet>

Which, when run against your input, will create this output:

<?xml version="1.0" encoding="UTF-8"?>
<section>
   <ss_start/>
   <p id="ss_main">aa</p>
   <p id="ss_chap">bb</p>
   <ss_end/>
   <p id="main">cc</p>
   <p id="main">dd</p>
   <p id="main">ee</p>
   <ss_start/>
   <p id="ss_main">ff</p>
   <ss_end/>
   <p id="main">gg</p>
   <p id="main">hh</p>
   <p id="main">ii</p>
   <p id="main">jj</p>
   <ss_start/>
   <p id="ss_chap">xx</p>
   <p id="ss_main">yy</p>
   <p id="ss_chap">zz</p>
   <ss_end/>
</section>

I see now that you tagged your question with xslt-2.0, which means you can use grouping. I'll try to update with an example in XSLT 2.0.

XSLT 2.0 group-adjacent

In XSLT 2.0, you can use a boolean true/false as the the group-adjacent grouping key as follows, which is quite a bit shorter than the XSLT 1.0 code above:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    version="2.0">

    <xsl:output indent="yes" />

    <xsl:template match="node() | @*">
        <xsl:copy>
            <xsl:apply-templates select="node() | @*" />
        </xsl:copy>
    </xsl:template>

    <xsl:template match="section">
        <xsl:copy>
            <xsl:for-each-group select="*" group-adjacent="starts-with(@id, 'ss')">
                <xsl:if test="current-grouping-key()"><ss_start /></xsl:if>
                <xsl:apply-templates select="current-group()" />
                <xsl:if test="current-grouping-key()"><ss_end /></xsl:if>
            </xsl:for-each-group>
        </xsl:copy>
    </xsl:template>

</xsl:stylesheet>