Merge pull request #1076 from levje/levje/filter_by_length_fix

[FIX]: Return rejected streamlines with empty sft

scilpy/tractograms/streamline_operations.py

@@ -408,19 +408,16 @@ def filter_streamlines_by_length(sft, min_length=0., max_length=np.inf,
         valid_length_ids = np.logical_and(lengths >= min_length,
                                           lengths <= max_length)
         filtered_sft = sft[valid_length_ids]
-
-        if return_rejected:
-            rejected_sft = sft[~valid_length_ids]
     else:
-        valid_length_ids = []
+        valid_length_ids = np.array([], dtype=bool)
         filtered_sft = sft
 
     # Return to original space
     sft.to_space(orig_space)
     filtered_sft.to_space(orig_space)
 
     if return_rejected:
-        rejected_sft.to_space(orig_space)
+        rejected_sft = sft[~valid_length_ids]
         return filtered_sft, valid_length_ids, rejected_sft
     else:
         return filtered_sft, valid_length_ids

scilpy/tractograms/tests/test_streamline_operations.py

@@ -7,6 +7,7 @@
 import pytest
 from dipy.io.streamline import load_tractogram
 from dipy.tracking.streamlinespeed import length
+from dipy.io.stateful_tractogram import StatefulTractogram
 
 from scilpy import SCILPY_HOME
 from scilpy.io.fetcher import fetch_data, get_testing_files_dict
@@ -174,6 +175,17 @@ def test_filter_streamlines_by_length():
     # Test that streamlines shorter than 100 and longer than 120 were removed.
     assert np.all(lengths >= min_length) and np.all(lengths <= max_length)
 
+    # === 4. Return rejected streamlines with empty sft ===
+    empty_sft = short_sft[[]]  # Empty sft from short_sft (chosen arbitrarily)
+    filtered_sft, _, rejected = \
+        filter_streamlines_by_length(empty_sft, min_length=min_length,
+                                     max_length=max_length,
+                                     return_rejected=True)
+    assert isinstance(filtered_sft, StatefulTractogram)
+    assert isinstance(rejected, StatefulTractogram)
+    assert len(filtered_sft) == 0
+    assert len(rejected) == 0
+
 
 def test_filter_streamlines_by_total_length_per_dim():
     long_sft = load_tractogram(in_long_sft, in_ref)