Resolve "Minimal sample size in train-, val, test-set"

Closes #76 (closed)

src/data_handling/data_preparation.py

@@ -354,7 +354,6 @@ class DataPrep(object):
             intersect = reduce(np.intersect1d, (non_nan_history.coords[dim].values, non_nan_label.coords[dim].values, non_nan_observation.coords[dim].values))
 
         min_length = self.kwargs.get("min_length", 0)
-        length = len(intersect)
         if len(intersect) < max(min_length, 1):
             self.history = None
             self.label = None