Apply affine inplace when the underlying arraysequence of the streamlines is not a sliced view.

Author: MarcCote

nibabel/streamlines/array_sequence.py

@@ -146,6 +146,10 @@ def __init__(self, iterable=None, buffer_size=4):
 
         self.extend(iterable)
 
+    @property
+    def is_sliced_view(self):
+        return self._lengths.sum() != self._data.shape[0]
+
     @property
     def is_array_sequence(self):
         return True

nibabel/streamlines/tractogram.py

@@ -429,8 +429,12 @@ def apply_affine(self, affine, lazy=False):
         if np.all(affine == np.eye(4)):
             return self  # No transformation.
 
-        for i in range(len(self.streamlines)):
-            self.streamlines[i] = apply_affine(affine, self.streamlines[i])
+        if self.streamlines.is_sliced_view:
+            # Apply affine only on the selected streamlines.
+            for i in range(len(self.streamlines)):
+                self.streamlines[i] = apply_affine(affine, self.streamlines[i])
+        else:
+            self.streamlines._data = apply_affine(affine, self.streamlines._data, inplace=True)
 
         if self.affine_to_rasmm is not None:
             # Update the affine that brings back the streamlines to RASmm.