Sensor Filter: Ignore the first values after ESP boot

[thEngal]

Describe the problem you have/What new integration you would like
I need a filter that ignores incoming values for a specified time after ESP bootup.

Please describe your use case for this integration and alternatives you've tried:
I want to add a gas sensor (MQ-135) which needs a specified time to heat up. With this filter, the heat up values wouldn’t passed forward to Home Assistant.

Additional context

[marklister]

One could probably accomplish this with a simple lambda filter looking at sensor.uptime...

[CarlosGS]

I am missing this too ;(

When using sliding_window_moving_average and send_first_at to guarantee a filtered value, the first odd reading (right after rebooting) introduces a distorted sample, which is annoying.

A parameter like n_skip: 1 or n_ignore: 1 would be awesome IMHO.

[nkvoll]

I've worked around a similar issue on one of my devices by doing something along these lines to skip the first couple of measurements during boot:

substitutions:
  my_sensor: my_sensor

esphome:
  #...
  on_boot:
    # work around https://github.com/esphome/feature-requests/issues/607
    # set a default value for the skip counter, otherwise it's nan
    - sensor.template.publish:
        id: ${my_sensor}_skips
        state: 0

#...

# register sensors for the datapoints
sensor:
  - platform: my-platform
    name: ${my_sensor}
    filters:
      # work around https://github.com/esphome/feature-requests/issues/607
      # increment a skip counter, this skips the first two measurements 
      - lambda: auto s = id(${my_sensor}_skips); if(s->state > 2) { return x; } else { s->publish_state(s->state+1); return {}; }

  # work around https://github.com/esphome/feature-requests/issues/607
  # create a skip counter
  - platform: template
    id: ${my_sensor}_skips
    internal: true
    accuracy_decimals: 0

It's not very pretty, and a simple skip-filter would be great for this use-case where a sensor's startup values may be off.