How to get the intersection of two xpath node sets

Question

To get a union of two different node sets I can do the following using the | separator:

node.xpath(
    '(//C:Year[not(@value="2019")]) | (//R:Product[@value="Phone"])'
    , namespaces={'C': 'Columns', 'R': 'Rows'})

Is there a way to get an intersection between the two without knowing the relationship between those two paths (i.e., allowing them to be ordered any way). I tried the following:

node.xpath('(//C:Year[not(@value="2019")]) and (//R:Product[@value="Phone"])', namespaces={'C': 'Columns', 'R': 'Rows'})

But the and seems to return a bool instead of a node set. What would be the proper way to do this?

I'm not sure a good place to share xml/xpath expressions but you can go here https://extendsclass.com/xpath-tester.html and copy-paste in the following xpath and xml and it should work fine:

Expression: //C:Year[not(@value="2019")] | //R:Product[@value="Phone"]
XML:        <Data xmlns:R="Rows" xmlns:C="Columns" xmlns:V="Values"><R:ProductGroup value="Electronics"><R:Product value="Computer"><C:Year value="2018"><V:SumOfRevenue value="104"/><V:SumOfUnits   value="3"/></C:Year><C:Year value="2019"><V:SumOfRevenue value="82"/><V:SumOfUnits   value="9"/></C:Year><C:Year value="(all)"><V:SumOfRevenue value="186"/><V:SumOfUnits   value="12"/></C:Year></R:Product><R:Product value="Phone"><C:Year value="2018"><V:SumOfRevenue value="102"/><V:SumOfUnits   value="4"/></C:Year><C:Year value="2019"><V:SumOfRevenue value="99"/><V:SumOfUnits   value="12"/></C:Year><C:Year value="(all)"><V:SumOfRevenue value="201"/><V:SumOfUnits   value="16"/></C:Year></R:Product><R:Product value="(all)"><C:Year value="2018"><V:SumOfRevenue value="206"/><V:SumOfUnits   value="7"/></C:Year><C:Year value="2019"><V:SumOfRevenue value="181"/><V:SumOfUnits   value="21"/></C:Year><C:Year value="(all)"><V:SumOfRevenue value="387"/><V:SumOfUnits   value="28"/></C:Year></R:Product></R:ProductGroup><R:ProductGroup value="Media"><R:Product value="Movies"><C:Year value="2018"><V:SumOfRevenue value="25"/><V:SumOfUnits   value="12"/></C:Year><C:Year value="2019"><V:SumOfRevenue value="26"/><V:SumOfUnits   value="13"/></C:Year><C:Year value="(all)"><V:SumOfRevenue value="51"/><V:SumOfUnits   value="25"/></C:Year></R:Product><R:Product value="Theater"><C:Year value="2018"><V:SumOfRevenue value="17"/><V:SumOfUnits   value="3"/></C:Year><C:Year value="2019"><V:SumOfRevenue value="20"/><V:SumOfUnits   value="6"/></C:Year><C:Year value="(all)"><V:SumOfRevenue value="37"/><V:SumOfUnits   value="9"/></C:Year></R:Product><R:Product value="(all)"><C:Year value="2018"><V:SumOfRevenue value="42"/><V:SumOfUnits   value="15"/></C:Year><C:Year value="2019"><V:SumOfRevenue value="46"/><V:SumOfUnits   value="19"/></C:Year><C:Year value="(all)"><V:SumOfRevenue value="88"/><V:SumOfUnits   value="34"/></C:Year></R:Product></R:ProductGroup><R:ProductGroup value="(all)"><R:Product value="(all)"><C:Year value="2018"><V:SumOfRevenue value="248"/><V:SumOfUnits   value="22"/></C:Year><C:Year value="2019"><V:SumOfRevenue value="227"/><V:SumOfUnits   value="40"/></C:Year><C:Year value="(all)"><V:SumOfRevenue value="475"/><V:SumOfUnits   value="62"/></C:Year></R:Product></R:ProductGroup></Data>

One possible solution is to 'go back to the root' for each intersection by using ancestor::RootName, so we would have:

//C:Year[not(@value="2019")]/ancestor::Data//R:Product[@value="Phone"]

Is there another way to do this?

Answer 1

In XPath 2.0, use the intersect operator.

There's no simple way of doing it in XPath 1.0

I'm wondering though whether you really want the intersection. The intersection of a set of C:Year elements with a set off R:Product elements is going to be empty (no element can be a member of both sets -- it can be a C:Year or an R:Product but not both.).

So I suspect that what you want isn't actually the set intersection, but something else. But I can't work out what you want from your question.