Trend sensor too brittle on HA restart because it has no minimum duration option #39179
Description
The problem
The Trend sensor's sample_duration and max_samples options let you track "long-term" trends (meaning anything trend involving more than 2 sample points). However, all samples are deleted upon HA restart, and the sensor starts trying to fit trends the first 2 samples it gets and often "detects" a trend, which defeats the whole purpose of setting these options.
A min_duration attribute is required on the Trend sensor to make the existing options make sense. In fact, the current options are not very useful. It's certain that most people using the Trend sensor with multiple samples want the trend to be over a certain amount of time, nothing more and nothing less. Otherwise, the findings would be quite useless. A "trend" involving multiple samples that meets a required change gradient tells you nothing unless you know over how long of a period that trend is happening.
The ideal solution: The sample_duration and max_samples options should be removed entirely because a binary sensor tracking trend just doesn't make sense over a variable amount of time. They should be replaced with a single, optional duration. If it's not set, then the Trend will just track trends between the current state and the immediately preceding state, as is already the case. If it is set, then the Trend will track the trend over the set duration, and will not falsely fire when the required length of samples is unavailable (like when HA restarts).
The temporary, non-breaking solution: Add a min_duration option that will add to the effect of the existing sample_duration and max_samples options by simply mandating that the binary sensor not fire when the collected data does not span the minimum duration specified (like when HA restarts). This is a stopgap solution and a no-brainer.
Environment
- Home Assistant Core release with the issue: 0.114
- Last working Home Assistant Core release (if known): N/A
- Operating environment (OS/Container/Supervised/Core): Container
- Integration causing this issue: Trend
- Link to integration documentation on our website: https://www.home-assistant.io/integrations/trend
Problem-relevant configuration.yaml
- platform: trend
sensors:
outside_suddenly_cool:
entity_id: sensor.outside_temperature
friendly_name: "Outside Suddenly Cool"
device_class: cold
sample_duration: 1200
max_samples: 20
min_gradient: -0.00241