I have an XML:
...
I need to group together the nodes which have the same key and then I
need to add the attribute "val" in all such cases.

So, The output I need is:
...
How do I go about doing this? I am using Xalan and XSLT 1.0.
...
I have used the Meunichian method to group the nodes with same keys
together.

T:\ftemp>type harsh.xml
<?xml version="1.0" encoding="UTF-8"?>
<first>
    <second>
        <a val="4" key="one">b</a>
        <a val="2" key="two">b</a>
    </second>
    <second>
        <a val="3" key="one">c</a>
    </second>
</first>

T:\ftemp>type harsh.xsl
<?xml version="1.0" encoding="US-ASCII"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                version="1.0">

<xsl:template match="/">
  <op>
    <xsl:for-each select="//*[@key]
                          [generate-id(.)=generate-id(key('keys',@key)[1])]">
      <xsl:element name="{@key}">
        <val><xsl:value-of select="sum(key('keys',@key)/@val)"/></val>
      </xsl:element>
    </xsl:for-each>
  </op>
</xsl:template>

T:\ftemp>xslt harsh.xml harsh.xsl con
<?xml version="1.0" encoding="utf-8"?>
<op>
   <one>
      <val>7</val>
   </one>
   <two>
      <val>2</val>
   </two>
</op>
T:\ftemp>

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