Question

I’m using the last() function to try to get the last entry in my xml as so:

//Name[last()]

however, it is returning the list to me rather than just the last name in the document… any suggestions?

thanks

Answer 1

This is a common gotcha due to what “//” stands for. Many people assume it stands for the descendant axis, but it actually stands for /descendant-or-self::node()/.

//Name[last()] is short for /descendant-or-self::node()/Name[last()], which makes more obvious the fact that this expression actually contains two steps:

1. /descendant-or-self::node(), which selects the context node and all its descendants, and
2. Name[last()], which selects the last <Name> child of the context node.

Step #2 is evaluated once for each node returned by step 1. If step 1 returns 10 nodes, than step 2 (and thus the entire expression) can return up to 10 nodes as well.

If you instead encapsulate the expression with parentheses, you can use an “expression filter” rather than a “step filter”: (//Name)[last()]

This ensures that the entire expression will return no more than 1 <Name> element, specifically, the last one in document order among all the elements returned by the expression to its left.

For more details and nuances, check out this email thread: http://markmail.org/thread/otd3iz5lag72emq4#query:+page:1+mid:qdsrmjrbbdvve3c3+state:results

And this article: http://developer.marklogic.com/blog/xpath-punctuation-part-5