Append text to each string in array in template

I’ve been trying DRY up some of my wordier templates a bit now that you no longer have to explicitly write out the name of each entity you want tracked and ran across an unexpected limitation. I feel like there has to be a better way to do this in Jinja but I can’t figure it out for the life of me. Since I know there’s a lot of Jinja wizards on here I’m hoping someone can help me out.

Basically I have a bunch of sensors with a very similar naming convention, group.person_detected_<room name>. I’m trying to make a sensor which is true when group.anyone is home and the person_detected group is off for a set of rooms. I originally made the sensor as one long if <state> and <state> and <state> and ... statement to ensure each entity name was written out. Now since you don’t have to I want to stop repeating the group.person_detected_ part.

I came up with this:

{% set detectors = (['', 'upstairs', 'guest_room', 'bedroom'] | join(' group.person_detected_')).split(' ')[1:] %}
{{ is_state('group.anyone', 'home') and expand(detectors) | selectattr('state', 'eq', 'on') | list | length == 0 }}

This works but its kind of ugly. All I want to do is have an array with a list of room names and then use a filter or function to prefix each element of that array with some text. I couldn’t seem to figure out anyway to do that besides that kind of hacky join then split.

So basically, is there a better way to add text to each string element in array in Jinja? Or maybe a custom filter added to Jinja in Home Assistant?


I know this is an old topic, but it was the top result of my google search.

I think I found a better way to do it.

{{ ["test1", "test2", "test3"] | map("regex_replace", "^", "sensor.") | list }}


['sensor.test1', 'sensor.test2', 'sensor.test3']

It uses a simple regex to replace the beginning of each string (^).

The same technique could also be used to add a suffix:

{{ ["test1", "test2", "test3"] | map("regex_replace", "$", ".suffix") | list }}
['test1.suffix', 'test2.suffix', 'test3.suffix']
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