Question

I’m trying to count the occurrences of every value for a specific attribute (e.g. @root) of every element that matches a query. Some of these matching elements do not have the attribute, but I want to count those as well (i.e. also list the amount of matched elements that did not have the attribute)

Currently I use this, but this does not match the nodes that dont have a root attribute. The counting is done by the application, which allows me to show intermediate results.

    //node[@rel='su']/@root

I want something like

    //node[@rel='su']/string(if .[@root] then @root else 'fallback-value')

The queries are run against Berkeley DB XML so XPath2 and XQuery might also be used to solve this.

edit: To clarify, I am looking for a query which treats the non-existence of the @root attribute as a special case; i.e. as if the attribute did exist and had ‘fallback-value’ as value.

Answer 1

Try this:

//node[@rel='su']/(@root/string(), 'no-value')[1]

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Follows the original answer to the misunderstood question

Why don’t you just use

//node[@rel='su']

then? It will match both node elements that have a @root attribute and those who do not.

Given that a node can have at most one @root attributes, counting the nodes is enough.