ix bug that caused weighted cf.collapse and cf.weights to fail when a cell meausures has a size 1 axis

Changelog.rst

@@ -5,6 +5,9 @@ Version NEXTVERSION
 
 * Fix bug in `cf.read` that prevented some OPeNDAP URLS being read
   (https://github.com/NCAS-CMS/cf-python/issues/948)
+* Fix bug that caused weighted `cf.collapse` and `cf.weights` to fail
+  when a cell meausures has a size 1 axis
+  (https://github.com/NCAS-CMS/cf-python/issues/952)
 
 ----
 

MANIFEST.in

@@ -9,7 +9,7 @@ recursive-exclude cf/data *.rst
 prune cf/test
 recursive-include cf/test __init__.py test_*.py 
 recursive-include cf/test cfa_test.sh run_tests.py setup_create_field.py create_test_files*.py individual_tests.sh
-recursive-include cf/test test_file.nc test_file[2-4].nc file.nc file[1-9].nc ugrid_global_1.nc ugrid_global_2.nc create_test_files.npz create_test_files_2.npz wgdos_packed.pp extra_data.pp file1.pp *.cdl create_test_files.npz create_test_files_2.npz example_field_0.nc
+recursive-include cf/test test_file.nc test_file[2-4].nc file.nc file[1-9].nc ugrid_global_1.nc ugrid_global_2.nc create_test_files.npz create_test_files_2.npz wgdos_packed.pp extra_data.pp file1.pp *.cdl create_test_files.npz create_test_files_2.npz example_field_0.nc cell_measures.nc
 recursive-include cf/test/example_field_0.zarr[23] *
 include cf/test/example_field_0.kerchunk
 prune cf/test/dir

cf/test/test_collapse.py

@@ -37,6 +37,9 @@ def setUp(self):
         self.filename2 = os.path.join(
             os.path.dirname(os.path.abspath(__file__)), "test_file2.nc"
         )
+        self.cell_measures = os.path.join(
+            os.path.dirname(os.path.abspath(__file__)), "cell_measures.nc"
+        )
 
     def test_Field_collapse_CLIMATOLOGICAL_TIME(self):
         verbose = False
@@ -853,6 +856,31 @@ def test_Field_collapse_HEALPix(self):
             g1.coordinate_reference("grid_mapping_name:latitude_longitude")
         )
 
+    def test_Field_cell_measures(self):
+        """Test collapse weights by area and volume cell measures."""
+        f = cf.read(self.cell_measures)[0]
+        self.assertEqual(f.shape, (1, 5, 5, 5))
+        self.assertEqual(f.cell_measure("measure:area").shape, (5, 5))
+        self.assertEqual(f.cell_measure("measure:volume").shape, (1, 5, 5, 5))
+
+        f.collapse("area: mean", weights="area")
+        f.collapse("volume: mean", weights="volume")
+
+        self.assertEqual(f.weights("area").shape, (5, 5))
+        self.assertEqual(f.weights("volume").shape, (5, 5, 5))
+
+        g = f[..., 0]
+
+        self.assertEqual(g.shape, (1, 5, 5, 1))
+        self.assertEqual(g.cell_measure("measure:area").shape, (5, 1))
+        self.assertEqual(g.cell_measure("measure:volume").shape, (1, 5, 5, 1))
+
+        g.collapse("area: mean", weights="area")
+        g.collapse("volume: mean", weights="volume")
+
+        self.assertEqual(g.weights("area").shape, (5,))
+        self.assertEqual(g.weights("volume").shape, (5, 5))
+
 
 if __name__ == "__main__":
     print("Run date:", datetime.datetime.now())

cf/weights.py

@@ -1548,9 +1548,9 @@ def cell_measure(
                 )
 
         clm = clm.get_data(_fill_value=False).copy()
-        if clm_axes != clm_axes0:
-            iaxes = [clm_axes0.index(axis) for axis in clm_axes]
-            clm.squeeze(iaxes, inplace=True)
+
+        # Squeeze out size 1 axes
+        clm.squeeze(inplace=True)
 
         if methods:
             weights[tuple(clm_axes)] = measure + " cell measure"