Question

In this question i asked how to perform a conditional increment. The provided answer worked, but does not scale well on huge data-sets.

The Input:

<Users>
    <User>
        <id>1</id>
        <username>jack</username>
    </User>
    <User>
        <id>2</id>
        <username>bob</username>
    </User>
    <User>
        <id>3</id>
        <username>bob</username>
    </User>
    <User>
        <id>4</id>
        <username>jack</username>
    </User>
</Users>

The desired output (in optimal time-complexity):

<Users>
   <User>
      <id>1</id>
      <username>jack01</username>
   </User>
   <User>
      <id>2</id>
      <username>bob01</username>
   </User>
   <User>
      <id>3</id>
      <username>bob02</username>
   </User>
   <User>
      <id>4</id>
      <username>jack02</username>
   </User>
</Users>

For this purpose it would be nice to

• sort input by username
• for each user
  • when previous username is equals current username
    • increment counter and
    • set username to ‘$username$counter’
  • otherwise
    • set counter to 1
• (sort by id again – no requirement)

Any thoughts?

Answer 1

This transformation produces exactly the specified wanted result and is efficient (O(N)):

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

 <xsl:key name="kUserByName" match="User" use="username"/>
 <xsl:key name="kUByGid" match="u" use="@gid"/>

 <xsl:variable name="vOrderedByName">
  <xsl:for-each select=
  "/*/User[generate-id()=generate-id(key('kUserByName',username)[1])]">
     <xsl:for-each select="key('kUserByName',username)">
       <u gid="{generate-id()}" pos="{position()}"/>
     </xsl:for-each>
  </xsl:for-each>
 </xsl:variable>

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

 <xsl:template match="username/text()">
     <xsl:value-of select="."/>
     <xsl:variable name="vGid" select="generate-id(../..)"/>

     <xsl:for-each select="ext:node-set($vOrderedByName)[1]">
      <xsl:value-of select="format-number(key('kUByGid', $vGid)/@pos, '00')"/>
     </xsl:for-each>
 </xsl:template>
</xsl:stylesheet>

When applied on the provided XML document:

<Users>
    <User>
        <id>1</id>
        <username>jack</username>
    </User>
    <User>
        <id>2</id>
        <username>bob</username>
    </User>
    <User>
        <id>3</id>
        <username>bob</username>
    </User>
    <User>
        <id>4</id>
        <username>jack</username>
    </User>
</Users>

the wanted, correct result is produced:

<Users>
   <User>
      <id>1</id>
      <username>jack01</username>
   </User>
   <User>
      <id>2</id>
      <username>bob01</username>
   </User>
   <User>
      <id>3</id>
      <username>bob02</username>
   </User>
   <User>
      <id>4</id>
      <username>jack02</username>
   </User>
</Users>