Variable combining several lists

Is there any way to define a variable as being the combination of several lists. For example, define “database_clients” as being the combination of all items in groups[‘app_servers’] and groups[‘processors’]. I’d rather define it once rather than use with_items in different places to combine them.

I looked at set_fact (http://docs.ansible.com/set_fact_module.html), but don’t think it’s possible that way.

you can define in hosts file

[database_clients:children]
processors
app_servers

or in other ways groups[‘processors’]|union(groups[‘app_servers’])

That works, thanks.