[Fix] ppg_plot() was not returning matplotlib.Figure

[luisqtr]

Hi...

Description

I needed to store the results of ppg_plot() in a file on disk (easier to inspect than doing it manually in the notebook). However, the function did not return the object matplotlib.figure so I could use fig.savefig([path]), even though the documentation says that it returns a figure.

If the PR is accepted, I can check similar behavior for the other variables.

Proposed Changes

• Return the object matplotlib.figure.Figure for ppg_plot() instead of just plotting the image on the notebook.
• [Docs] Minor edit: Added description about feature LFHF returned by hrv_frequency(), it was missing.

Checklist

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• I have read the CONTRIBUTING file.
• My PR is targetted 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)

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[codecov-commenter]

Codecov Report

Merging #678 (16311e9) into dev (0bc49ca) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              dev     #678      +/-   ##
==========================================
- Coverage   52.42%   52.38%   -0.04%     
==========================================
  Files         276      276              
  Lines       12424    12430       +6     
==========================================
- Hits         6513     6512       -1     
- Misses       5911     5918       +7     

Impacted Files	Coverage Δ
neurokit2/ecg/ecg_plot.py	90.47% <ø> (ø)
neurokit2/emg/emg_plot.py	97.77% <ø> (ø)
neurokit2/eog/eog_plot.py	92.15% <ø> (ø)
neurokit2/hrv/hrv_frequency.py	61.70% <ø> (ø)
neurokit2/ppg/ppg_plot.py	13.79% <ø> (ø)
neurokit2/rsp/rsp_plot.py	93.87% <ø> (ø)
neurokit2/signal/signal_plot.py	66.66% <ø> (ø)
neurokit2/rsp/rsp_simulate.py	93.75% <0.00%> (-4.47%)	⬇️
neurokit2/signal/signal_detrend.py	37.70% <0.00%> (-0.48%)	⬇️
neurokit2/signal/signal_filter.py	64.89% <0.00%> (ø)
... and 5 more

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[DominiqueMakowski]

Thanks for that PR, unfortunately, we recently changed that behaviour on behaviour to not return the figure, as it was causing some issues, among which double figures showing up in the console and inconsistent return type which is not a good programming practice (that said, it's possible that documentation has to be adjusted in some places!)

In principle thanks to the arcanes of matplotlib you can still recover the figure and save it to disk as follows:

import matplotlib.pyplot as plt
import neurokit2 as nk

# Generate 15 seconds of PPG signal (recorded at 250 samples / second)
ppg = nk.ppg_simulate(duration=15, sampling_rate=250, heart_rate=70, random_state=333)

# Process it
signals, info = nk.ppg_process(ppg, sampling_rate=250)

# Visualize the processing
nk.ppg_plot(signals, sampling_rate=250)

# Save it
plt.tight_layout()
plt.savefig("ppg.png", dpi=300)

Or even

fig = plt.gcf()
fig.set_size_inches(10, 6, forward=True)
fig.savefig("ppg2.png", dpi=300)

Let us know if it works, and if it does, you can edit your PR to just leave the documentation fix :)

[luisqtr]

Thanks for your feedback 😁. Your example code to save the plots worked very well!
I have updated the docs related with plot functions, deleting the Return and adding an example to save figures to PNG files.

[luisqtr]

Apparently there is an error building the new docs induced by my change in ecg_plot(). This is the first time doing a PR and working with sphinx, so I am not completely sure what went wrong 😅. How can I reproduce locally the Documentation check before doing a new commit?

[DominiqueMakowski]

I fixed the issues, merging now :) thanks!

[welcome]

Congrats on merging your first pull request! 🎉🍾 We're looking forward to your next one!