How do I generate a comma-separated list with XSLT/XPath?

Question

This is a pretty common pattern:

<xsl:for-each select="*">
   <xsl:value-of select="."/>
   <xsl:if test="position() != last()">
      <xsl:text>,</xsl:text>
   </xsl:if>
</xsl:for-each>

Take a look at the position(), count() and last() functions; e.g., test="position() < last()".

For an XSLT 2.0 option, you can use the separator attribute on xsl:value-of.

This xsl:value-of:

<xsl:value-of select="/root/item" separator=", "/>

would produce this output:

apple, orange, banana

You could also use more than just a comma for a separator. For example, this:

<xsl:text>'</xsl:text>
<xsl:value-of select="/root/item" separator="', '"/>
<xsl:text>'</xsl:text>

Would produce the following output:

'apple', 'orange', 'banana'

Another XSLT 2.0 option is string-join()...

<xsl:value-of select="string-join(/*/item,', ')"/>

<xsl:if test="following-sibling::*">,</xsl:if>

or (perhaps more efficient, but you'd have to test):

<xsl:for-each select="*[1]">
   <xsl:value-of select="."/>
   <xsl:for-each select="following-sibling::*">
       <xsl:value-of select="concat(',',.)"/>
   </xsl:for-each>
</xsl:for-each>

A simple XPath 1.0 one-liner:

     concat(., substring(',', 2 - (position() != last())))

Put it into this transformation:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output method="text"/>

    <xsl:template match="/*">
      <xsl:for-each select="*">
        <xsl:value-of select=
         "concat(., substring(',', 2 - (position() != last())))"
         />
      </xsl:for-each>
    </xsl:template>
</xsl:stylesheet>

and apply it to the XML document:

<root>
    <item>apple</item>
    <item>orange</item>
    <item>banana</item>
</root>

to get the wanted result:

apple,orange,banana

EDIT:

Here is a comment from Robert Rossney to this answer:

That's pretty opaque code for a human to read. It requires you to know two non-obvious things about XSLT: 1) what the substring function does if its index is out of range and 2) that logical values can be implicitly converted to numerical ones.

and here is my answer:

Guys, never shy from learning something new. In fact this is all Stack Overflow is about, isn't it? :)

Robert gave the classis not(position() = last()) answer. This requires you to process the whole current node list to get context size, and in large input documents this might make the conversion consume more memory. Therefore, I normally invert the test to be the first thing

<xsl:for-each select="*">
  <xsl:if test="not(position() = 1)>, </xsl:if>
  <xsl:value-of select="."/>   
</xsl:for-each>