XSLT to flatten XML

Question

Could anyone please help me with the following transformation?

Here is the input xml:

<?xml version="1.0" encoding="UTF-8"?>
<book>
    <title>My book</title>
    <pages>200</pages>
    <size>big</size>
    <author>
        <name>Smith</name>
    </author>
    <author>
        <name>Wallace</name>
    </author>
    <author>
        <name>Brown</name>
    </author>
</book>
<book>
    <title>Other book</title>
    <pages>100</pages>
    <size>small</size>
    <author>King</author>
</book>
<book>
    <title>Pretty book</title>
    <pages>150</pages>
    <size>medium</size>
</book>

This is the desired output

<book style="even">
    <title>My book</title>
    <pages>200</pages>
    <size>big</size>
    <author-name>Smith</author-name>
</book>
<book style="odd">
    <title>My book</title>
    <pages>200</pages>
    <size>big</size>
    <author-name>Wallace</author-name>
</book>
<book style="even">
    <title>My book</title>
    <pages>200</pages>
    <size>big</size>
    <author-name>Brown</author-name>
</book>
<book style="odd" >
    <title>Other book</title>
    <pages>100</pages>
    <size>small</size>
    <author-name>King</author-name>
</book>
<book style="even">
    <title>Pretty book</title>
    <pages>150</pages>
    <size>medium</size>
    <author-name />
</book>

I tried using xsl:for-each loops, but I suppose they brought me to a dead end. The tricky part here is the "style" attribute that somehow needs to be "global" no matter how many author tags are placed in any book.

Answer 1

This simple, pure XSLT 1.0 transformation (no conditionals, no xsl:for-each, no parameter passing, no xsl:element, no use of the infamously inefficient //):

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 xmlns:my="my:my" exclude-result-prefixes="my" >
    <xsl:output omit-xml-declaration="yes" indent="yes"/>
    <xsl:strip-space elements="*"/>

    <my:names>
     <n>odd</n>
     <n>even</n>
    </my:names>

    <xsl:variable name="vStyles"
        select="document('')/*/my:names/*"/>

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

    <xsl:template match="book/author">
     <xsl:variable name="vPos">
      <xsl:number level="any" count="book/author|book[not(author)]"/>
     </xsl:variable>
        <book style="{$vStyles[$vPos mod 2 +1]}">
          <xsl:copy-of select="@*|../node()[not(self::author)]"/>
          <author-name>
            <xsl:value-of select="normalize-space()"/>
      </author-name>
        </book>
    </xsl:template>

    <xsl:template match="book[author]">
     <xsl:apply-templates/>
    </xsl:template>

    <xsl:template match="book[not(author)]">
     <xsl:variable name="vPos">
      <xsl:number level="any" count="book/author|book[not(author)]"/>
     </xsl:variable>
        <book style="{$vStyles[$vPos mod 2 +1]}">
          <xsl:copy-of select="@*|node()"/>
          <author-name/>
        </book>
    </xsl:template>

    <xsl:template match="book[author]/*[not(self::author)]"/>
</xsl:stylesheet>

when applied to this XML document (the provided one wrapped into a single top element):

<t>
    <book>
        <title>My book</title>
        <pages>200</pages>
        <size>big</size>
        <author>
            <name>Smith</name>
        </author>
        <author>
            <name>Wallace</name>
        </author>
        <author>
            <name>Brown</name>
        </author>
    </book>
    <book>
        <title>Other book</title>
        <pages>100</pages>
        <size>small</size>
        <author>King</author>
    </book>
    <book>
        <title>Pretty book</title>
        <pages>150</pages>
        <size>medium</size>
    </book>
</t>

produces exactly the wanted, correct result:

<t>
   <book style="even">
      <title>My book</title>
      <pages>200</pages>
      <size>big</size>
      <author-name>Smith</author-name>
   </book>
   <book style="odd">
      <title>My book</title>
      <pages>200</pages>
      <size>big</size>
      <author-name>Wallace</author-name>
   </book>
   <book style="even">
      <title>My book</title>
      <pages>200</pages>
      <size>big</size>
      <author-name>Brown</author-name>
   </book>
   <book style="odd">
      <title>Other book</title>
      <pages>100</pages>
      <size>small</size>
      <author-name>King</author-name>
   </book>
   <book style="even">
      <title>Pretty book</title>
      <pages>150</pages>
      <size>medium</size>
      <author-name/>
   </book>
</t>

Explanation: Appropriate use of xsl:number and templates/pattern matching.

Answer 2

This stylesheet first stores all author nodes as well as all book nodes without authors in a global variable. "/." sorts them in document order. Then the main template iterates over all nodes in this variable and generates output according to the position in the sequence.

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:variable name="authors" select="(//author | //book[not(author)])/."/>

  <xsl:template match="/">
    <xsl:element name="result">
      <xsl:for-each select="$authors">
        <xsl:apply-templates select=".">
          <xsl:with-param name="position" select="position()+1"/>
        </xsl:apply-templates>
      </xsl:for-each>
    </xsl:element>
  </xsl:template>

  <xsl:template match="text()|title|pages|size">
    <xsl:copy>
      <xsl:apply-templates/>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="book">
    <xsl:param name="position" select="1"/>
    <xsl:element name="book">
      <xsl:attribute name="style">
        <xsl:if test="$position mod 2 = 0">even</xsl:if>
        <xsl:if test="$position mod 2 = 1">odd</xsl:if>
      </xsl:attribute>
      <xsl:apply-templates select="title"/>
      <xsl:apply-templates select="pages"/>
      <xsl:apply-templates select="size"/>
      <xsl:element name="author-name"/>
    </xsl:element>
  </xsl:template>

  <xsl:template match="author">
    <xsl:param name="position" select="1"/>
    <xsl:element name="book">
      <xsl:attribute name="style">
        <xsl:if test="$position mod 2 = 0">even</xsl:if>
        <xsl:if test="$position mod 2 = 1">odd</xsl:if>
      </xsl:attribute>
      <xsl:apply-templates select="../title"/>
      <xsl:apply-templates select="../pages"/>
      <xsl:apply-templates select="../size"/>
      <xsl:element name="author-name">
        <xsl:if test="name">
          <xsl:value-of select="name"/>
        </xsl:if>
        <xsl:if test="not(name)">
          <xsl:value-of select="."/>
        </xsl:if>
      </xsl:element>
    </xsl:element>
  </xsl:template>
</xsl:stylesheet>