[Feature Request] move pandas to extras

[psarka]

🚀 Suggestion

Move pandas dependency to extras.

Motivation

Pandas is a heavy dependency, doing very little for stable baselines and quite annoying when running on a device such as Nvidia Jetson, as I need to build a wheel for it myself. I may find time to contribute this movement, if you would be interested.

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[Miffyli]

Good point and I agree with this (heavy dependency for little functionality). @araffin what is your view on this? We could (potentially?) replace all panda functionality with other dependency-free code, unless that breaks some backwards-compatibility stuff. Changing the dependencies would also cause bit of headache to people (e.g. somebody takes an older project that does not sb3 version [they should have!], and now logger stuff would not work out of the box).

[psarka]

I inspected the code, so let me make a more precise suggestion:

pandas is used only in three places:

• monitor/load_results
• logger/read_json
• logger/read_csv

The last two functions are only used in tests, so they could be moved there. load_results is only used in results_plotter.

matplotlib, another dependency that I would like not to have, is only used in two places:

• logger/Figure
• results_plotter

in logger/Figure it is only used as a type annotation, so easy to do without.

That leaves the results_plotter as the only user of both pandas and matplotlib. So my updated proposal would be to:

• move read_json to tests
• move read_csv to tests
• move load_results to results_plotter
• move pandas and matplotlib to optional dependencies in the extra section, with the impact that results_plotter will no longer work with base installation. Logger will still work.
• if needed, add pandas to optional dependencies tests section.

[araffin]

Hello, rather than changing the install behavior, I would be more in favor of making SB3 run without pandas and matplotlib, so when you install it with pip install --no-deps flag. That would mean doing lazy import of pandas inside load_results (and other helpers) and using if typing.TYPE_CHECKING in the logger.