return metric score along with untrained best models & params

darts/models/forecasting/forecasting_model.py

@@ -569,7 +569,7 @@ def gridsearch(
         verbose=False,
         n_jobs: int = 1,
         n_random_samples: Optional[Union[int, float]] = None,
-    ) -> Tuple["ForecastingModel", Dict]:
+    ) -> Tuple["ForecastingModel", Dict[str, Any], float]:
         """
         Find the best hyper-parameters among a given set using a grid search.
 
@@ -660,9 +660,10 @@ def gridsearch(
 
         Returns
         -------
-        ForecastingModel, Dict
+        ForecastingModel, Dict, float
             A tuple containing an untrained `model_class` instance created from the best-performing hyper-parameters,
-            along with a dictionary containing these best hyper-parameters.
+            along with a dictionary containing these best hyper-parameters,
+            and metric score for the best hyper-parameters.
         """
         raise_if_not(
             (forecast_horizon is not None)
@@ -707,7 +708,7 @@ def gridsearch(
             zip(params_cross_product), verbose, total=len(params_cross_product)
         )
 
-        def _evaluate_combination(param_combination):
+        def _evaluate_combination(param_combination) -> float:
             param_combination_dict = dict(
                 list(zip(parameters.keys(), param_combination))
             )
@@ -748,9 +749,11 @@ def _evaluate_combination(param_combination):
                 )
                 error = metric(pred, val_series)
 
-            return error
+            return float(error)
 
-        errors = _parallel_apply(iterator, _evaluate_combination, n_jobs, {}, {})
+        errors: List[float] = _parallel_apply(
+            iterator, _evaluate_combination, n_jobs, {}, {}
+        )
 
         min_error = min(errors)
 
@@ -760,7 +763,7 @@ def _evaluate_combination(param_combination):
 
         logger.info("Chosen parameters: " + str(best_param_combination))
 
-        return model_class(**best_param_combination), best_param_combination
+        return model_class(**best_param_combination), best_param_combination, min_error
 
     def residuals(
         self, series: TimeSeries, forecast_horizon: int = 1, verbose: bool = False

darts/tests/models/forecasting/test_4theta.py

@@ -62,7 +62,7 @@ def test_best_model(self):
         series = sine_series + linear_series
         train_series, val_series = series.split_before(series.time_index[-10])
         thetas = np.linspace(-3, 3, 30)
-        best_model, _ = FourTheta.select_best_model(train_series, thetas)
+        best_model, _, _ = FourTheta.select_best_model(train_series, thetas)
         model = FourTheta(
             random.choice(thetas),
             model_mode=random.choice(list(ModelMode)),

darts/tests/models/forecasting/test_backtesting.py

@@ -46,7 +46,7 @@ def compare_best_against_random(model_class, params, series, stride=1):
 
     # instantiate best model in expanding window mode
     np.random.seed(1)
-    best_model_1, _ = model_class.gridsearch(
+    best_model_1, _, _ = model_class.gridsearch(
         params,
         series,
         forecast_horizon=10,
@@ -57,7 +57,9 @@ def compare_best_against_random(model_class, params, series, stride=1):
 
     # instantiate best model in split mode
     train, val = series.split_before(series.time_index[-10])
-    best_model_2, _ = model_class.gridsearch(params, train, val_series=val, metric=mape)
+    best_model_2, _, _ = model_class.gridsearch(
+        params, train, val_series=val, metric=mape
+    )
 
     # intantiate model with random parameters from 'params'
     random.seed(1)
@@ -343,6 +345,7 @@ def test_gridsearch_random_search(self):
 
         self.assertEqual(type(result[0]), RandomForest)
         self.assertEqual(type(result[1]["lags"]), int)
+        self.assertEqual(type(result[2]), float)
         self.assertTrue(min(param_range) <= result[1]["lags"] <= max(param_range))
 
     @unittest.skipUnless(TORCH_AVAILABLE, "requires torch")
@@ -433,12 +436,12 @@ def test_gridsearch_n_jobs(self):
             parameters = test["parameters"]
 
             np.random.seed(1)
-            _, best_params1 = model.gridsearch(
+            _, best_params1, _ = model.gridsearch(
                 parameters=parameters, series=ts_train, val_series=ts_val, n_jobs=1
             )
 
             np.random.seed(1)
-            _, best_params2 = model.gridsearch(
+            _, best_params2, _ = model.gridsearch(
                 parameters=parameters, series=ts_train, val_series=ts_val, n_jobs=-1
             )