Added reorder sort string, which sorts variables alphabetically. (ecm…

…wf#144)

* Added reorder sort string, which sorts variables alphabetically. Crucial for pre-training and transfer learning.

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src/anemoi/datasets/data/dataset.py

@@ -261,13 +261,19 @@ def _drop_to_columns(self, vars):
         return sorted([v for k, v in self.name_to_index.items() if k not in vars])
 
     def _reorder_to_columns(self, vars):
+        if isinstance(vars, str) and vars == "sort":
+            # Sorting the variables alphabetically.
+            # This is cruical for pre-training then transfer learning in combination with
+            # cutout and adjust = 'all'
+
+            indices = [self.name_to_index[k] for k, v in sorted(self.name_to_index.items(), key=lambda x: x[0])]
+            assert set(indices) == set(range(len(self.name_to_index)))
+            return indices
+
         if isinstance(vars, (list, tuple)):
             vars = {k: i for i, k in enumerate(vars)}
 
-        indices = []
-
-        for k, v in sorted(vars.items(), key=lambda x: x[1]):
-            indices.append(self.name_to_index[k])
+        indices = [self.name_to_index[k] for k, v in sorted(vars.items(), key=lambda x: x[1])]
 
         # Make sure we don't forget any variables
         assert set(indices) == set(range(len(self.name_to_index)))