[BUG] KeyError when using custom root name

[aakashparsi]

Describe the bug
When I'm using a custom root name rather than total, I've got KeyError: total from the forecast_proportions method.

To Reproduce

hts.HTSRegressor(model = 'auto_arima', revision_method = 'FP', n_jobs = 0)
htsmodel.fit(trainSet, hierarchy, root = 'TotalWeight')
htsfit.predict(steps_ahead = forecast_horizon)

Error Trace

KeyError Traceback (most recent call last)
in
----> 1 pred = htsfit.predict(steps_ahead = forecast_horizon)

~/.local/lib/python3.6/site-packages/hts/core/regressor.py in predict(self, exogenous_df, steps_ahead, distributor, disable_progressbar, show_warnings, **predict_kwargs)
350 self.hts_result.errors = (key, error)
351 self.hts_result.residuals = (key, residual)
--> 352 return self._revise(steps_ahead=steps_ahead)
353
354 def _revise(self, steps_ahead: int = 1) -> pandas.DataFrame:

~/.local/lib/python3.6/site-packages/hts/core/regressor.py in _revise(self, steps_ahead)
357 forecasts=self.hts_result.forecasts,
358 mse=self.hts_result.errors,
--> 359 nodes=self.nodes,
360 )
361

~/.local/lib/python3.6/site-packages/hts/revision.py in revise(self, forecasts, mse, nodes)
77
78 elif self.name == MethodT.FP.name:
---> 79 return forecast_proportions(forecasts, nodes)
80
81 else:

~/.local/lib/python3.6/site-packages/hts/functions.py in forecast_proportions(forecasts, nodes)
223 fore_sum = fore_sum[:, np.newaxis]
224 if column == 0:
--> 225 rev_top = np.array(forecasts["total"].yhat)
226 rev_top = rev_top[:, np.newaxis]
227 else:

KeyError: 'total'

Desktop (please complete the following information):

• OS: Windows
• scikit-hts version: 0.5.11
• Python version: 3.6.9

Additional context
Perhaps, the total in the forecast_proportions method should be replaced with the root parameter passed in the fit method.

[carlomazzaferro]

Seems like the right diagnostic. Every instance of hardcoded "root" in the functions.py file should be replaced via param. I'm backed up, you think you could give this a go? @aakashparsi

[aakashparsi]

I think I can spend some time on this later next week due to the current work items I have for this week.