Migrate to PyTorch

[kiudee]

Description

Replaces Tensorflow v1.x with PyTorch 1.8. The most important neural network learners have been converted:

• FATE
• FETA
• CmpNet
• RankNet

In order to fully support scikit-learn interoperability, we also include skorch now as dependency.

The old master branch corresponding to v1.x.y will be continued here to facilitate bug fixes: https://github.com/kiudee/cs-ranking/tree/v1.x

Motivation and Context

The code base depends heavily on Tensorflow v1, which is no longer updated due to the major update to Tensorflow v2. Since a major rewrite to support Tensorflow v2 would have been necessary, we deliberated whether it is better to switch over to PyTorch instead. Finally, we decided to go for PyTorch, since we also switched to it on other projects and the momentum of the research community is currently behind it.

Special thanks go to @timokau who worked hard on making this migration a reality.

How Has This Been Tested?

The tests of the learners have been adapted to use PyTorch. The tests were run locally and on GitHub Actions to confirm that everything passes.

Does this close/impact existing issues?

Resolves #125, resolves #153, resolves #146, fixes #130, closes #105, closes #43.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have added tests to cover my changes.

[codecov[bot]]

Codecov Report

Merging #191 (7c1f922) into master (1217c46) will decrease coverage by 4.90%. The diff coverage is 87.94%.

@@            Coverage Diff             @@
##           master     #191      +/-   ##
==========================================
- Coverage   57.04%   52.14%   -4.91%     
==========================================
  Files         113      102      -11     
  Lines        6560     5090    -1470     
==========================================
- Hits         3742     2654    -1088     
+ Misses       2818     2436     -382     

Impacted Files	Coverage Δ
csrank/choicefunction/__init__.py	100.00% <ø> (ø)
csrank/choicefunction/baseline.py	37.93% <0.00%> (-1.36%)	:arrow_down:
csrank/constants.py	100.00% <ø> (ø)
csrank/core/__init__.py	100.00% <ø> (ø)
csrank/dataset_reader/dataset_reader.py	68.57% <ø> (+27.39%)	:arrow_up:
csrank/dataset_reader/discretechoice/util.py	22.41% <ø> (+6.89%)	:arrow_up:
...nk/dataset_reader/letor_listwise_dataset_reader.py	14.56% <ø> (ø)
...ank/dataset_reader/letor_ranking_dataset_reader.py	14.52% <ø> (ø)
csrank/dataset_reader/util.py	36.44% <ø> (+18.64%)	:arrow_up:
csrank/discretechoice/__init__.py	100.00% <ø> (ø)
... and 87 more