[R-package] introduce Dataset methods set_field() and get_field()

[jameslamb]

Contributes to #4543, as part of #4310.

This PR proposes the following changes in the R package:

• deprecates Dataset$getinfo() (with a warning its name will be changed to get_field())
• deprecates Dataset$setinfo() (with a warning its name will be changed to set_field())
• adds method Dataset$get_field(field_name) to Dataset, matching the Python package

  • LightGBM/python-package/lightgbm/basic.py

    Line 1939 in 8a90ea3

    def get_field(self, field_name):

• adds method Dataset$set_field(field_name, data) should be added to Dataset, matching the Python package

  • LightGBM/python-package/lightgbm/basic.py

    Line 1890 in 8a90ea3

    def set_field(self, field_name, data):

Notes for Reviewers

I only added new tests, but left existing tests with getinfo() and setinfo() in place, so that those methods are still tested as long as they exist in the package.

[StrikerRUS]

Not sure whether we should update here
https://github.com/microsoft/LightGBM/blob/master/docs/FAQ.rst#i-used-setinfo-tried-to-print-my-lgb-dataset-and-now-the-r-console-froze. WDYT?

Update Dataset$setinfo() here

LightGBM/R-package/R/lgb.Dataset.R

Line 557 in 54facc4

, "To modify attributes like 'init_score', use Dataset$setinfo(). "

[jameslamb]

Update Dataset$setinfo() here

Done in a745987

Not sure whether we should update here
https://github.com/microsoft/LightGBM/blob/master/docs/FAQ.rst#i-used-setinfo-tried-to-print-my-lgb-dataset-and-now-the-r-console-froze. WDYT?

I think it's ok to leave that alone for now, since the functions are being deprecated but not removed yet. That entire FAQ section probably deserves some updates and revisions, to check if the issues listed there still exist in recent versions. But that could be done in a separate PR.

[jameslamb]

iiinteresting, I see this error on the lint job

Some R documentation files have changed. Please re-generate them and commit those changes.

I did re-generate the docs before pushing. Maybe there was a new release of {roxygen2} or something. I'll investigate this later today!

[jameslamb]

Maybe there was a new release of {roxygen2} or something

Yes, there was a new release (7.1.2) a few days ago: https://cran.r-project.org/web/packages/roxygen2/index.html.

But it also looks like there are a few local changes I forgot to git add 😆

Regenerated the docs with {roxygen} 7.1.2 and added the requested changes in e92a28e

[shiyu1994]

Shall we also update here in the FAQ documentation? Will set_field encounter the same problem?

[shiyu1994]

Other modifications LGTM. They seem to be simple renaming. And thanks @StrikerRUS for detecting the minor mistakes.

[jameslamb]

Shall we also update here in the FAQ documentation? Will set_field encounter the same problem?

ah! I answered this in #4571 (comment) actually. I don't think we need to worry about it for this PR. That particular question was added in #976 (4 years ago), so it might not even be relevant any more. I'd prefer to take updating the FAQ as a separate task.

[StrikerRUS]

LGTM! Thanks a lot for working on this!

[github-actions]

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