XQuery/XPath: Using count() and max() function for return of element with highest count

Question

I have an XML file that contains authors and editors.

<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="file:textbook.rnc" type="compact"?>
<books xmlns="books">

    <book ISBN="i0321165810" publishername="OReilly">
        <title>XPath</title>
        <author>
            <name>
                <fname>Priscilla</fname>
                <lname>Walmsley</lname>
            </name>
        </author>
        <year>2007</year>
        <field>Databases</field>
    </book>

    <book ISBN="i0321165812" publishername="OReilly">
        <title>XQuery</title>
        <author>
           <name>
               <fname>Priscilla</fname>
               <lname>Walmsley</lname>
            </name>
        </author>
        <editor>
            <name>
                <fname>Lisa</fname>
                <lname>Williams</lname>
            </name>
        </editor>
        <year>2003</year>
        <field>Databases</field>
    </book>

    <publisher publishername="OReilly">
        <web-site>www.oreilly.com</web-site>
        <address>
            <street_address>hill park</street_address>
            <zip>90210</zip>
            <state>california</state>
        </address>
        <phone>400400400</phone>
        <e-mail>[email protected]</e-mail>
        <contact>
            <field>Databases</field>
            <name>
                <fname>Anna</fname>
                <lname>Smith</lname>
            </name>
        </contact>
    </publisher>
</books>

I'm looking for a way to return the person who has been listed the most times as an author and/or editor. The solution should be XQuery 1.0 (XPath 2.0) compatible.

I was thinking about using a FLWOR query to iterate through all authors and editors, then doing a count of unique authors/editors, then returning the author(s)/editor(s) that match the highest count. But I haven't been able to find the proper solution.

Does anyone have any suggestion as to how such a FLWOR query would be written? Could this be done in a simpler way, using XPath?

Answer 1

This may help:

declare default element namespace 'books';
(for $name in distinct-values($doc/books/*/*/name)
 let $entries := $doc/books/*[data(*/name) = $name]
 order by count($entries) descending
 return $entries/*/name)[1]

Answer 2

Here is a pure XPath 2.0 expression, admittedly not for the faint-hearted:

(for $m in max(for $n in distinct-values(/*/b:book/(b:author | b:editor)
                                        /b:name/concat(b:fname, '|', b:lname)),
               $cnt in count(/*/b:book/(b:author | b:editor)
                             /b:name[$n eq concat(b:fname, '|', b:lname) ])
               return $cnt
               ),
     $name in /*/b:book/(b:author | b:editor)/b:name,
     $fullName in $name/concat(b:fname, '|',  b:lname),
     $count in count( /*/b:book/(b:author | b:editor)
                   /b:name[$fullName eq concat(b:fname, '|',  b:lname)])
  return
     if($count eq $m)
       then $name
       else ()
   )[1]

where the prefix "b:" is associated with the namespace "books".

XSLT 2.0 - based verification:

<xsl:stylesheet version="2.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 xmlns:b="books">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>
 <xsl:strip-space elements="*"/>

 <xsl:template match="/">
   <xsl:sequence select=
   "(for $m in max(for $n in distinct-values(/*/b:book/(b:author | b:editor)
                                            /b:name/concat(b:fname, '|', b:lname)),
                   $cnt in count(/*/b:book/(b:author | b:editor)
                                 /b:name[$n eq concat(b:fname, '|', b:lname) ])
                   return $cnt
                   ),
         $name in /*/b:book/(b:author | b:editor)/b:name,
         $fullName in $name/concat(b:fname, '|',  b:lname),
         $count in count( /*/b:book/(b:author | b:editor)
                       /b:name[$fullName eq concat(b:fname, '|',  b:lname)])
      return
         if($count eq $m)
           then $name
           else ()
       )[1]
   "/>
 </xsl:template>
</xsl:stylesheet>

when this transformation is applied on the provided XML document:

<books xmlns="books">
    <book ISBN="i0321165810" publishername="OReilly">
        <title>XPath</title>
        <author>
            <name>
                <fname>Priscilla</fname>
                <lname>Walmsley</lname>
            </name>
        </author>
        <year>2007</year>
        <field>Databases</field>
    </book>
    <book ISBN="i0321165812" publishername="OReilly">
        <title>XQuery</title>
        <author>
            <name>
                <fname>Priscilla</fname>
                <lname>Walmsley</lname>
            </name>
        </author>
        <editor>
            <name>
                <fname>Lisa</fname>
                <lname>Williams</lname>
            </name>
        </editor>
        <year>2003</year>
        <field>Databases</field>
    </book>
    <publisher publishername="OReilly">
        <web-site>www.oreilly.com</web-site>
        <address>
            <street_address>hill park</street_address>
            <zip>90210</zip>
            <state>california</state>
        </address>
        <phone>400400400</phone>
        <e-mail>[email protected]</e-mail>
        <contact>
            <field>Databases</field>
            <name>
                <fname>Anna</fname>
                <lname>Smith</lname>
            </name>
        </contact>
    </publisher>
</books>

the wanted, correct name element is selected and output:

<name xmlns="books">
   <fname>Priscilla</fname>
   <lname>Walmsley</lname>
</name>