dev

Changelog.rst

@@ -256,8 +256,8 @@ version 3.11.0
 * Fix for `cf.aggregate` failures when a datum or coordinate
   conversion parameter has an array value
   (https://github.com/NCAS-CMS/cf-python/issues/230)
-* Allow for regridding using a destination field featuring size 1 dimension(s)
-  (https://github.com/NCAS-CMS/cf-python/issues/250)
+* Allow for regridding using a destination field featuring size 1
+  dimension(s) (https://github.com/NCAS-CMS/cf-python/issues/250)
 * Fix bug that sometimes caused `cf.Field.autocyclic` to fail when
   setting a construct that is cyclic and has a defined period
 * Fix bug that sometimes caused a failure when reading PP extra data

cf/__init__.py

@@ -75,7 +75,7 @@
 
 __Conventions__ = "CF-1.11"
 __date__ = "2023-??-??"
-__version__ = "3.16.0"
+__version__ = "3.17.0"
 
 _requires = (
     "numpy",

cf/data/dask_regrid.py

@@ -287,18 +287,25 @@ def regrid(
     a = a.reshape(non_regrid_shape + tuple(dst_shape))
 
     n_dst_axes = len(dst_shape)
+
     if n_src_axes == n_dst_axes:
         pass
     elif n_src_axes == 1 and n_dst_axes > 1:
         # E.g. UGRID regridded to regular lat-lon; changes
         #      'axis_order' from [0,2,1] to [0,3,1,2]
-        r = axis_order[-1]
-        axis_order = [i + n_dst_axes - 1 if i > r else i for i in axis_order]
-        axis_order[-1:] = range(r, r + n_dst_axes)
-    elif n_dst_axes == 1 and n_src_axes > 1:
+        raxis = axis_order[-1]
+        axis_order = [
+            i if i <= raxis else i + n_dst_axes - 1 for i in axis_order
+        ]
+        axis_order[-1:] = range(raxis, raxis + n_dst_axes)
+    elif n_src_axes == 2 and n_dst_axes == 1:
         # E.g. regular lat-lon regridded to UGRID; changes
-        #      'axis_order' from [0,3,2,1] to [0,2,1]
-        pass  # TODOUGRID
+        #      'axis_order' from [0,2,4,5,1,3] to [0,2,3,4,1], or
+        #      [0,2,4,5,3,1] to [0,1,3,4,2]
+        raxis0, raxis = axis_order[-2:]
+        print(axis_order)
+        axis_order = [i if i <= raxis else i - 1 for i in axis_order[:-1]]
+        print(axis_order)
     else:
         raise ValueError("TODOUGRID")
 

cf/data/data.py

@@ -3734,6 +3734,7 @@ def _regrid(
         from .dask_regrid import regrid, regrid_weights
 
         shape = self.shape
+        ndim = self.ndim
         src_shape = tuple(shape[i] for i in regrid_axes)
         if src_shape != operator.src_shape:
             raise ValueError(
@@ -3755,12 +3756,17 @@ def _regrid(
 
         # Define the regridded chunksizes
         regridded_chunks = []  # The 'chunks' parameter to `map_blocks`
+        drop_axis = []  # The 'drop_axis' parameter to `map_blocks`
         new_axis = []  # The 'new_axis' parameter to `map_blocks`
         n = 0
         for i, c in enumerate(dx.chunks):
             if i in regridded_sizes:
                 sizes = regridded_sizes[i]
                 n_sizes = len(sizes)
+                if not n_sizes:
+                    drop_axis.append(i)
+                    continue
+
                 regridded_chunks.extend(sizes)
                 if n_sizes > 1:
                     new_axis.extend(range(n + 1, n + n_sizes))
@@ -3770,25 +3776,29 @@ def _regrid(
 
             n += 1
 
+        # Update the axis identifiers.
+        #
+        # This is necessary when regridding changes the number of data
+        # dimensions (e.g. as happens when regridding a mesh topology
+        # axis to/from separate lat and lon axes).
         if new_axis:
-            # Update the axis identifiers.
-            #
-            # This is necessary when regridding changes the number of
-            # data dimensions (e.g. as happens when regridding a mesh
-            # topology axis to separate lat and lon axes).
             axes = list(self._axes)
             for i in new_axis:
                 axes.insert(i, new_axis_identifier(tuple(axes)))
 
-            self._axes = tuple(axes)
+            self._axes = axes
+        elif drop_axis:
+            axes = self._axes
+            axes = [axes[i] for i in range(ndim) if i not in drop_axis]
+            self._axes = axes
 
         # Set the output data type
         if method in ("nearest_dtos", "nearest_stod"):
             dst_dtype = dx.dtype
         else:
             dst_dtype = float
 
-        non_regrid_axes = [i for i in range(self.ndim) if i not in regrid_axes]
+        non_regrid_axes = [i for i in range(ndim) if i not in regrid_axes]
 
         src_mask = operator.src_mask
         if src_mask is not None:
@@ -3813,6 +3823,7 @@ def _regrid(
             weights_dst_mask=weights_dst_mask,
             ref_src_mask=src_mask,
             chunks=regridded_chunks,
+            drop_axis=drop_axis,
             new_axis=new_axis,
             meta=np.array((), dtype=dst_dtype),
         )