Add a 'last' mode and attribute to min_max sensor

[markferry]

Add a 'last' mode and attribute to min_max sensor

Inspired by this question "Combining multiple sensor values into one with most recent wins strategy", provide a mode of min_max sensor to report only the most recent value received from a list of sensors. (Follows the nomenclature of Grafana for 'last' value of a sensor).

This solves the issue of multiple sensors providing intermittent and unsolicited readings of the same metric - multiple battery-powered temperature sensors within a room for example.

It does not identify which of the monitored sensors provided the most recent update.

The current workaround is a template sensor or virtual device (input_number or similar) with an automation to update the value when any of the monitored sensors triggers.

Pull request in home-assistant.github.io with documentation: home-assistant/home-assistant.io#4167

Example entry for configuration.yaml (if applicable):

# Example configuration.yaml entry
sensor:
  - platform: min_max
    type: last
    entity_ids:
      - sensor.kitchen_east_temperature
      - sensor.kitchen_west_temperature

Checklist:

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.github.io

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[homeassistant]

Hi @markferry,

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Once you do that we will be able to review and accept this pull request.

Thanks!

[tinloaf]

I don't think this should be part of the min_max sensor. It's conceptually different from min or max. This sensor shouldn't become a "collection of selection functions we could think of"-sensor. If we want this functionality, I think it should live in its own sensor.

[markferry]

To an extent, @tinloaf, I'm with you, though one could argue min_max sensor is misnamed since it already includes mean as a significant feature.
We might instead call it aggregate_sensor and allow many more modes, complementing statistics sensor which calculates various stats across multiple values of a single sensor.

But a much more ambitious change would instead expand how homogeneous groups work, providing something like OpenHABs AND, OR, AVG, SUM groups, etc.

[fabaff]

min_max is just a name. It's always possible to rename platforms if it makes sense and not happen every other release. If a new feature can be added with a couple of lines and it fits the purpose of an existing sensor then we should just add it.

[fabaff]

🐦