return single encoded covariates if called on single target

[dennisbader]

Summary

• fixes bug where add_encoders in RegressionModels was used in combination with a single target series in fit/predict
• SequentialEncoder (called by model's add_encoders) now returns covariates as single TimeSeries when called on single series

[dumjax]

good for me

[hrzn]

Thanks @dennisbader.
Do you know what was the impact? Were the encoders simply not working for single series (though I guess we would have cought it earlier)?

[dennisbader]

Reason was that SequentialEncoder always returned a list of TimeSeries even for single series input (@dumjax found this when testing for Shap integration).

For TorchForecastingModels this wasn't an issue as the series were internally converted to a list of series before using the encoders.
For RegressionModels the conversion isn't applied before the encodings are generated.

I only added RegressionModel encoder tests for the multi-ts case, which is why they didn't catch it.
Should I add another test for single-ts case?

[hrzn]

I only added RegressionModel encoder tests for the multi-ts case, which is why they didn't catch it.
Should I add another test for single-ts case?

If you have a moment, this is always welcome, so we make sure the issue does not reproduce again.

[hrzn]

As discussed, still to do:

• Transform everything as a list in RegressionModels
• Unify API for accessing model.encode_inference() in torch and regression models.

[dennisbader]

As discussed, still to do:

• Transform everything as a list in RegressionModels
• Unify API for accessing model.encode_inference() in torch and regression models.

I will open a new PR for these points as this is a bug fix.

If you have a moment, this is always welcome, so we make sure the issue does not reproduce again.

I checked and I had already added a test for single series in this PR:

darts/darts/tests/models/forecasting/test_regression_models.py

Line 1058 in 6ff4e22

# don't pass covariates, let them be generated by encoders. Test single target series input

[codecov-commenter]

Codecov Report

Base: 93.74% // Head: 93.73% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (6ff4e22) compared to base (28ca88d).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1193      +/-   ##
==========================================
- Coverage   93.74%   93.73%   -0.01%     
==========================================
  Files          83       83              
  Lines        8407     8398       -9     
==========================================
- Hits         7881     7872       -9     
  Misses        526      526              

Impacted Files	Coverage Δ
darts/utils/data/encoders.py	97.20% <100.00%> (+0.05%)	⬆️
darts/timeseries.py	92.23% <0.00%> (-0.07%)	⬇️
...arts/models/forecasting/torch_forecasting_model.py	87.45% <0.00%> (-0.05%)	⬇️
darts/models/forecasting/block_rnn_model.py	98.24% <0.00%> (-0.04%)	⬇️
darts/models/forecasting/nhits.py	99.27% <0.00%> (-0.01%)	⬇️
darts/datasets/__init__.py	100.00% <0.00%> (ø)

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