How to convert a sensor on-the-fly from date to delta t

[AleXSR700]

Hello everyone,
I am enjoying playing with plotly and I would like to transform a date sensor (last restart time) to a delta t (uptime).

I thought I could use lambda but I think my ayntax is not quite right yet.

type: custom:plotly-graph
entities:
  - entity: sensor.esp32_wroom_32d_devkitc_v4_1_last_restart_time
    lambda: (ys) => ys.map(y => now().timestamp - y)

Essentially the current time minus the sensors value should result in an uptime in seconds.

Could anybody help me understand where I am going wrong?

Thank you
Alex

P.S.: In case David is reading this, I think the indentation on the lambda example is off. At least they were showing bad indentation when I tried to start with them as templates.

---

Edit:
All credit to @dbuezas who solved the issue and explained my errors in the following posts. Please read if you are a noob like me. 😉
The solution is

type: custom:plotly-graph
entities:
  - entity: sensor.esp32_wroom_32d_devkitc_v4_1_last_restart_time
    line:
       shape: linear
    lambda: (ys,xs) => ys.map(((y,i) => (xs[i] - Date.parse(y))/1000)); #updated!
    unit_of_measurement: s

[dbuezas]

Try with:

 (ys) => ys.map(y => Date.now() - new Date(y))

You can check the js logs by opening the "dev console" in the browser. Makes easy to spot syntax errors and what not.

By the way, https://esphome.io/components/sensor/uptime.html

Thanks for noting the indentation error. I'll check it out soon. Can you point me to the exact example?

[AleXSR700]

Yes, I am trying to create a delta time, so an uptime sensor.
the last_restart_time will of course be constant for a long time (until the device restarts), so the value that is changing is of course the date.now()

So it should create a line with a constant slope (depending on the ratio between yaxis in seconds and xaxis in hours, days or whatever).

[dbuezas]

Got it.

Then you need to subtract the x axis, not Date.now() (or the python equivalent of now().timestamp). That will work in a template sensor because the value of "now" is stored in the db as time passes, but if you do that while plotting, then "now" is... well... now... for all datapoints :)
Try the yaml I sent above, it should do what you need

[AleXSR700]

Thank you for the explanation!
I tried your code but it is still a horizontal line (even after autoscale) and the y-axis is formatted as a date and not a number. If the value was being transformed to a number, the y-axis would automatically switch to number, correct?

[dbuezas]

oh, missed a parenthesis, try it again (I updated it)

[AleXSR700]

That's it, that's it! You solved it!
Thank you so so much!

[dbuezas]

Solution:

type: custom:plotly-graph
entities:
  - entity: sensor.esp32_wroom_32d_devkitc_v4_1_last_restart_time
    lambda: (ys) => ys.map((y => Date.now() - Date.parse(y))/1000)
    unit_of_measurement: s