input file:
<foo type="a"/>
<foo type="b"/>
<foo type="c"/>
<bar type="a"/>
<bar type="b"/>

Now, say I've got node sets:
<xsl:variable name="A" select="foo"/>
<xsl:variable name="B" select="bar"/>

And I'd like to select any <foo>s with types not found in the set of <bar>s. In this example, that would be just the 3rd <foo>. How would I do this?

My first thought was to select:
$A[string(@type) != string($B/@type)]

...but that will only select nodes from A whose type is not "a" (the first <foo>'s type).

Any clues?

Thanks,
Rich

You don't want or need string function and you need to change from != to not:
$A[not(@type = $B/@type)]

not means there are no matches, i.e. no @type in $B matches the @type of $A, != means they all don't match, if any non-match can be found then include the node.
If you're xml is:

and xsl is:
Run this and then change select to:
$A[@type != $B/@type]

to see difference.

--

Joe

Sorry, the initial xsl should have been:
I pasted the wrong version...

--

Joe

The whole problem is in the "magical" properties of the "!=" operator and in the use of the "string" function here.
Look why your code is not working:
The function "string" returns the string value of the first node when the argument is a nodeset. So in your XPath expression you compare the context node's attribute's string-value to the first "foo" element's attribute value.
Even is not working again due to the rules for "!=" operator. Actually, "=" operator "returns" true for nodesets NS1 and NS2 as arguments when there is a node n1 in NS1 and node n2 in NS2 such that their string-values are the same. And "!=" is not a logical negation of "=": for 2 nodesets "!=" "returns" true if there is at least one pair of (n1, n2) [n1 is in NS1 and n2 is in NS2] such that their string-values are not the same. Therefore there are situations when "not(NS1 = NS2)" is not equivalent to "NS1 != NS2".
That's why you have to use "not" instead of "!=" here and you have to compare nodesets instead of using"string" function.

The working XPath expression is Regards,
Armen

Wow, thanks for setting me straight, guys!

I have a similar issue but I'm having a hard time trying to figure out how to make it work. I'm trying to get the union of two node sets with one having priority.

Example:
<defaults>
  <color>red</color>
  <size>10</size>
  <flavor>cherry</flavor>
</defaults>

<config>
  <color>black</color>
  <flavor>blueberry</flavor>
</config>

So, it seems like I should be able to do something like this:

<xsl:variable name="class" select="defaults"></xsl:param>
<xsl:variable name="instance" select="config"></xsl:param>

<xsl:for-each select="$class[not(name() != $instance/name())]">
    <xsl:text>#x0a;</xsl:text><xsl:copy-of select="."/>
</xsl:for-each>

<xsl:for-each select="$instance">
        <xsl:copy-of select="."/>
</xsl:for-each>

The results should end up something like this then:

  <size>10</size>
  <color>black</color>
  <flavor>blueberry</flavor>

I know I've probably presented this too simply so please let me know what other info I could provide to help it make sense. The main issue seems to be the predicate not being allowed to match on name().

You first need to say whether you are using XSLT 1.0 or XSLT 2.0.

In 2.0 this is best treated as a grouping problem:

<xsl:for-each-group select="defaults/*, config/*" group-by="node-name()">
  <xsl:copy-of select="current-group()[last()]"/>
</xsl:for-each>

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

I'm using XSLT 1.0