Please try this XSL -

<?xml version="1.0"?> 
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
version="1.0">
 
<xsl:output method="xml" indent="yes" /> 
 
<xsl:template match="/root">
  <part12>
    <res>
       <!-- merging part1/a[1]/b and part2/w[1]/ss -->
       <xsl:choose>
         <xsl:when test="count(part1/a[1]/b) > count(part2/w[1]/ss)">         
            <xsl:for-each select="part2/w[1]/ss">
              <xsl:variable name="pos" select="position()" />
              <r><xsl:value-of select="." /><xsl:text> 
</xsl:text><xsl:value-of select="../../../part1/a[1]/b[$pos]" /></r>
            </xsl:for-each>
            <xsl:for-each select="part1/a[1]/b[position() > 
count(part2/w[1]/ss)]">
              <r><xsl:value-of select="." /></r>
            </xsl:for-each>
         </xsl:when>
         <xsl:when test="count(part1/a[1]/b) < count(part2/w[1]/ss)">         
	   <xsl:for-each select="part1/a[1]/b">
             <xsl:variable name="pos" select="position()" />
             <r><xsl:value-of select="../../../part2/w[1]/ss[$pos]" 
/><xsl:text> </xsl:text><xsl:value-of select="." /></r>
           </xsl:for-each>
           <xsl:for-each select="part2/w[1]/ss[position() > 
count(../../../part1/a[1]/b)]">
             <r><xsl:value-of select="." /></r>
           </xsl:for-each>       
         </xsl:when>
         <xsl:otherwise>         
	   <xsl:for-each select="part1/a[1]/b">
             <xsl:variable name="pos" select="position()" />
             <r><xsl:value-of select="../../../part2/w[1]/ss[$pos]" 
/><xsl:text> </xsl:text><xsl:value-of select="." /></r>
           </xsl:for-each>       
         </xsl:otherwise>
       </xsl:choose>
       
       <!-- merging part1/a[2]/b and part2/w[2]/ss -->
       <xsl:choose>
         <xsl:when test="count(part1/a[2]/b) > count(part2/w[2]/ss)">
           <xsl:for-each select="part2/w[2]/ss">
             <xsl:variable name="pos" select="position()" />
             <r><xsl:value-of select="." /><xsl:text> 
</xsl:text><xsl:value-of select="../../../part1/a[2]/b[$pos]" /></r>
           </xsl:for-each>
           <xsl:for-each select="part1/a[2]/b[position() > 
count(part2/w[2]/ss)]">
             <r><xsl:value-of select="." /></r>
           </xsl:for-each>     
         </xsl:when>
         <xsl:when test="count(part1/a[2]/b) < count(part2/w[2]/ss)">
       	   <xsl:for-each select="part1/a[2]/b">
             <xsl:variable name="pos" select="position()" />
             <r><xsl:value-of select="../../../part2/w[2]/ss[$pos]" 
/><xsl:text> </xsl:text><xsl:value-of select="." /></r>
           </xsl:for-each>
           <xsl:for-each select="part2/w[2]/ss[position() > 
count(../../../part1/a[2]/b)]">
             <r><xsl:value-of select="." /></r>
           </xsl:for-each>            
         </xsl:when>
         <xsl:otherwise>
           <xsl:for-each select="part1/a[2]/b">
             <xsl:variable name="pos" select="position()" />
             <r><xsl:value-of select="../../../part2/w[2]/ss[$pos]" 
/><xsl:text> </xsl:text><xsl:value-of select="." /></r>
           </xsl:for-each>           
         </xsl:otherwise>
       </xsl:choose>
    </res>
  </part12>
</xsl:template>
   
</xsl:stylesheet>

When the above XSL is applied to XML -

<root>
  <part1>
    <a>
      <b>AA</b><b>BB</b>
    </a>
    <a>
      <b>EE</b><b>FF</b><b>GG</b>
    </a>
  </part1>
  <part2>
    <w>
      <ss>a</ss><ss>b</ss><ss>c</ss><ss>d</ss>
    </w>
    <w>
      <ss>e</ss><ss>f</ss><ss>g</ss>
    </w>
  </part2>
</root>

The output produced is -

<?xml version="1.0" encoding="UTF-8"?>
<part12>
   <res>
      <r>a AA</r>
      <r>b BB</r>
      <r>c</r>
      <r>d</r>
      <r>e EE</r>
      <r>f FF</r>
      <r>g GG</r>
   </res>
</part12>

Regards,
Mukul


"MB" wrote:

> Hello. Please help me with solving such problem:
> I have input xml like this:
> 
> <root>
>   <part1>
>     <a>
>       <b> AA <b> <b> BB <b>
>     </a>
>     <a>
>       <b> EE <b> <b> FF <b> <b> GG <b>
>     </a>
>   </part1>
> 
>   <part2>
>     <w>
>       <ss> a </ss> <ss> b </ss> <ss> c </ss> <ss> d </ss>
>     </w>
>     <w>
>       <ss> e </ss> <ss> f </ss> <ss> g </ss>
>     </w>
>   </part2>
> 
> </root>
> ---------------------------------------------------------
> I need such output:
> <part12>
>   <res>
>     <r>a AA </r>
>     <r>b BB </r>
>     ...
>     <r>h HH </r>
>   <res>
> <part12>
> 
> Problem is that when I need to concatenate values from different trees
> I don't know how get the value of corresponded element from another
> tree.
> 
>