XSLT Cookbook

Determining if Two Nodes Are the Same

Problem

You need to determine if two separate references to a node are the same node.

Solution

If the compared nodes are element nodes with a unique attribute of type ID, then comparison is most conveniently made by comparing these attributes. If this is not the case, then use generate-id, as in:

<xsl:if test="generate-id($node1) = generate-id($node2)">

Here we assume $node1 and $node2 are node sets containing a single node.

An interesting generalization of this test checks if all the nodes in one node-set are the same as all the nodes in another. For this task, generate-id is not useful because it only generates an ID for the first node in document order. Instead, you need to take advantage the XPath union operator’s (|) ability to determine node equality.

<xsl:if test="count($ns1|$ns2) = count($ns1) and 
               count($ns1) = count($ns2)">

In other words, if two node sets have the same number of nodes, and the number of nodes resulting from the union of both node sets is the same as the number of nodes in one of those two original node sets, then they must be the same sets. If they are not, then the union must contain at least one more node than either individual set.

If you only care if $ns2 is either equal to or a subset of $ns1, then you can simply write:

<xsl:if test="count($ns1|$ns2) = count($ns1)">

On the other hand, if you want to test that $ns2 is a proper subset of $ns1, then you need to write:^[8]

<xsl:if test="count($ns1|$ns2) = count($ns1) ...