[feature] added PPG quality assessment functionality

[peterhcharlton]

Description

This PR aims at adding a new feature: PPG quality assessment. PPG quality assessment functionality has been added, and two initial quality assessment techniques have been included.

Proposed Changes

• Added ppg_quality.py
• Adjusted ppg_process.py to include quality assessment in the default processing pipeline
• Added details of the PPG quality assessment methods to ppg_methods.py

Checklist

• I have read the CONTRIBUTING file.
• My PR is targeted at the dev branch (and not towards the master branch).
• I ran the CODE CHECKS on the files I added or modified and fixed the errors.
• I have added the newly added features to News.rst (if applicable)

[danibene]

Hi @peterhcharlton , this is a really nice addition, thanks for your contribution! I think the tests may be failing because of the deletion of "PPG_Peaks" from the signals dataframe.

[danibene]

Did you intentionally delete this?

[DominiqueMakowski]

This should probably not be deleted

[danibene]

I added it back I think, not sure why it’s not showing up here: peterhcharlton@1cd76e4

[DominiqueMakowski]

Thanks Dani! Let's merge then :)

[peterhcharlton]

My apologies for not getting back to you sooner. Thank you for your work on this. To address the changes made:

• thanks for splitting the string to reduce the line length and splitting the text onto multiple lines.
• regarding "PPG_Peaks" in the PPG dataframe (in ppg_process.py): I can't immediately remember why I deleted this. However, I note two things:
  • there is a function named ppg_peaks as well as this entry in the dataframe. At one point I thought perhaps some errors I was encountering might be due to having a variable and a function both named ppg_peaks. Therefore, I used ppg_pw_peaks as the variable named (e.g. in ppg_quality.py). In reality, I don't know whether I needed to avoid using the same name for both the variable and the function, or whether I could have kept to using the same name.
  • the ECG dataframe (defined in ecg_process.py) does not appear to contain an entry for ECG peaks / R-waves.