Faster concatenation of cubes with AuxCoordFactorys (#6038)

* Faster concatenation of cubes with AuxCoordFactories

* Add whatsnew

Author: bouweandela

docs/src/whatsnew/latest.rst

@@ -83,6 +83,9 @@ This document explains the changes made to Iris for this release
 #. `@bouweandela`_ updated :meth:`iris.cube.CubeList.concatenate` so it keeps
    ancillary variables and cell measures lazy. (:pull:`6010`)
 
+#. `@bouweandela`_ made :meth:`iris.cube.CubeList.concatenate` faster for cubes
+   that have coordinate factories. (:pull:`6038`)
+
 🔥 Deprecations
 ===============
 

lib/iris/_concatenate.py

@@ -469,7 +469,7 @@ def name_key_func(factory):
 
         for factory in sorted(cube.aux_factories, key=name_key_func):
             coord = factory.make_coord(cube.coord_dims)
-            dims = cube.coord_dims(coord)
+            dims = factory.derived_dims(cube.coord_dims)
             metadata = _CoordMetaData(coord, dims)
             self.derived_metadata.append(metadata)
             coord_and_dims = _DerivedCoordAndDims(coord, tuple(dims), factory)