[BUG] Fixes a bug with SFAFast throwing an error when calling transform after fit (#2897)

* Bugfix for SFA_Fast with transform called after fit

Author: patrickzib

aeon/transformations/collection/dictionary_based/_sfa_fast.py

@@ -329,7 +329,7 @@ def _fit(self, X, y=None):
         self: object
         """
         # with parallel_backend("loky", inner_max_num_threads=n_jobs):
-        self._fit_transform(X, y, return_bag_of_words=False)
+        self._fit_transform(X, y, return_bag_of_words=self.return_sparse)
         return self
 
     def _transform(self, X, y=None):

aeon/transformations/collection/dictionary_based/tests/test_sfa.py

@@ -5,7 +5,8 @@
 import numpy as np
 import pytest
 
-from aeon.transformations.collection.dictionary_based._sfa import SFA
+from aeon.datasets import load_unit_test
+from aeon.transformations.collection.dictionary_based import SFA, SFAFast
 
 
 @pytest.mark.parametrize(
@@ -224,3 +225,27 @@ def test_typed_dict():
     word_list2 = p2.bag_to_string(p2.transform(X, y)[0][0])
 
     assert word_list == word_list2
+
+
+def test_sfa_fast_transform_after_fit():
+    """Test transform called after fit returns the same result as fit_transform()."""
+    X_train, y_train = load_unit_test(split="train")
+
+    # Fit, then transform
+    sfa = SFAFast()
+    sfa.fit(X_train, y_train)
+    x = sfa.transform(X_train, y_train)
+
+    # Fit_transform, then transform
+    sfa = SFAFast()
+    sfa.fit_transform(X_train, y_train)
+    y = sfa.transform(X_train, y_train)
+
+    # Assert that the two csr_matrix are equal
+    assert (
+        x.shape == y.shape
+        and x.dtype == y.dtype
+        and np.all(x.indices == y.indices)
+        and np.all(x.indptr == y.indptr)
+        and np.allclose(x.data, y.data)
+    )