Selecting groups in a hollow datatree using a string

What is your issue?

I'm using datatree to read in CORDEX formatted directories of climate data. As a small example I have a hollow datatree with the following groups:

dt2.groups

('/',
 '/BOM',
 '/BOM/ACCESS-CM2',
 '/BOM/ACCESS-CM2/ssp370',
 '/BOM/ACCESS-CM2/ssp126',
 '/BOM/ACCESS-CM2/historical',
 '/BOM/ACCESS-CM2/ssp370/r4i1p1f1',
 '/BOM/ACCESS-CM2/ssp126/r4i1p1f1',
 '/BOM/ACCESS-CM2/historical/r4i1p1f1',
 '/BOM/ACCESS-CM2/ssp370/r4i1p1f1/BARPA-R',
 '/BOM/ACCESS-CM2/ssp126/r4i1p1f1/BARPA-R',
 '/BOM/ACCESS-CM2/historical/r4i1p1f1/BARPA-R',
 '/BOM/ACCESS-CM2/ssp370/r4i1p1f1/BARPA-R/v1-r1-ACS-QME-AGCDv1-1960-2022',
 '/BOM/ACCESS-CM2/ssp126/r4i1p1f1/BARPA-R/v1-r1-ACS-QME-AGCDv1-1960-2022',
 '/BOM/ACCESS-CM2/historical/r4i1p1f1/BARPA-R/v1-r1-ACS-QME-AGCDv1-1960-2022',
 '/BOM/ACCESS-CM2/ssp370/r4i1p1f1/BARPA-R/v1-r1-ACS-QME-AGCDv1-1960-2022/day',
 '/BOM/ACCESS-CM2/ssp126/r4i1p1f1/BARPA-R/v1-r1-ACS-QME-AGCDv1-1960-2022/day',
 '/BOM/ACCESS-CM2/historical/r4i1p1f1/BARPA-R/v1-r1-ACS-QME-AGCDv1-1960-2022/day')

If I want to access only the leaves of the datatree that have historical in the group, is there a simple built in way to do it? I haven't been able to find anything in the documentation so far, and have come up with something rather clunky to do it myself:

def node_selector(dt_in,string_in):

    def node_selector_worker(self):
    
        if (string_in in str(self.groups)):
    
            return True
    
        return False

    return dt_in.filter(node_selector_worker)

This gives me a datatree that I can call leaves on:

node_selector(dt2,'historical').leaves

Cheers
Ben

Start by reading the DataTree.filter behavior and the groups and leaves accessors used in the example. Check how a node predicate is applied to hollow trees, then define the expected result as a tree whose leaves are limited to groups containing "historical" and verify that the built-in approach matches the shown custom selector.