Add decorator for skipping nodes without dimension

README.md

@@ -83,6 +83,58 @@ DataTree('multiscales', parent=None)
         image    (y, x) uint8 dask.array<chunksize=(16, 16), meta=np.ndarray>
 ```
 
+Map a function over datasets while skipping nodes that do not contain dimensions
+
+```python
+import numpy as np
+from spatial_image import to_spatial_image
+from multiscale_spatial_image import skip_non_dimension_nodes, to_multiscale
+
+data = np.zeros((2, 200, 200))
+dims = ("c", "y", "x")
+scale_factors = [2, 2]
+image = to_spatial_image(array_like=data, dims=dims)
+multiscale = to_multiscale(image, scale_factors=scale_factors)
+
+@skip_non_dimension_nodes
+def transpose(ds, *args, **kwargs):
+    return ds.transpose(*args, **kwargs)
+
+multiscale = multiscale.map_over_datasets(transpose, "y", "x", "c")
+print(multiscale)
+```
+
+A transposed MultiscaleSpatialImage.
+
+```
+<xarray.DataTree>
+Group: /
+├── Group: /scale0
+│       Dimensions:  (c: 2, y: 200, x: 200)
+│       Coordinates:
+│         * c        (c) int32 8B 0 1
+│         * y        (y) float64 2kB 0.0 1.0 2.0 3.0 4.0 ... 196.0 197.0 198.0 199.0
+│         * x        (x) float64 2kB 0.0 1.0 2.0 3.0 4.0 ... 196.0 197.0 198.0 199.0
+│       Data variables:
+│           image    (y, x, c) float64 640kB dask.array<chunksize=(200, 200, 2), meta=np.ndarray>
+├── Group: /scale1
+│       Dimensions:  (c: 2, y: 100, x: 100)
+│       Coordinates:
+│         * c        (c) int32 8B 0 1
+│         * y        (y) float64 800B 0.5 2.5 4.5 6.5 8.5 ... 192.5 194.5 196.5 198.5
+│         * x        (x) float64 800B 0.5 2.5 4.5 6.5 8.5 ... 192.5 194.5 196.5 198.5
+│       Data variables:
+│           image    (y, x, c) float64 160kB dask.array<chunksize=(100, 100, 2), meta=np.ndarray>
+└── Group: /scale2
+        Dimensions:  (c: 2, y: 50, x: 50)
+        Coordinates:
+          * c        (c) int32 8B 0 1
+          * y        (y) float64 400B 1.5 5.5 9.5 13.5 17.5 ... 185.5 189.5 193.5 197.5
+          * x        (x) float64 400B 1.5 5.5 9.5 13.5 17.5 ... 185.5 189.5 193.5 197.5
+        Data variables:
+            image    (y, x, c) float64 40kB dask.array<chunksize=(50, 50, 2), meta=np.ndarray>
+```
+
 Store as an Open Microscopy Environment-Next Generation File Format ([OME-NGFF])
 / [netCDF] [Zarr] store.
 

multiscale_spatial_image/__init__.py

@@ -7,9 +7,11 @@
     "Methods",
     "to_multiscale",
     "itk_image_to_multiscale",
+    "skip_non_dimension_nodes",
     "__version__",
 ]
 
 from .__about__ import __version__
 from .multiscale_spatial_image import MultiscaleSpatialImage
 from .to_multiscale import Methods, to_multiscale, itk_image_to_multiscale
+from .utils import skip_non_dimension_nodes

multiscale_spatial_image/utils.py

@@ -0,0 +1,24 @@
+from typing import Callable, Any
+from xarray import Dataset
+import functools
+
+
+def skip_non_dimension_nodes(
+    func: Callable[[Dataset], Dataset],
+) -> Callable[[Dataset], Dataset]:
+    """Skip nodes in Datatree that do not contain dimensions.
+
+    This function implements the workaround of https://github.com/pydata/xarray/issues/9693. In particular,
+    we need this because of our DataTree representing multiscale image having a root node that does not have
+    dimensions. Several functions need to be mapped over the datasets in the datatree that depend on having
+    dimensions, e.g. a transpose.
+    """
+
+    @functools.wraps(func)
+    def _func(ds: Dataset, *args: Any, **kwargs: Any) -> Dataset:
+        # check if dimensions are present otherwise return verbatim
+        if len(ds.dims) == 0:
+            return ds
+        return func(ds, *args, **kwargs)
+
+    return _func

test/test_utils.py

@@ -0,0 +1,23 @@
+import numpy as np
+from spatial_image import to_spatial_image
+from multiscale_spatial_image import skip_non_dimension_nodes, to_multiscale
+
+
+def test_skip_nodes():
+    data = np.zeros((2, 200, 200))
+    dims = ("c", "y", "x")
+    scale_factors = [2, 2]
+    image = to_spatial_image(array_like=data, dims=dims)
+    multiscale_img = to_multiscale(image, scale_factors=scale_factors)
+
+    @skip_non_dimension_nodes
+    def transpose(ds, *args, **kwargs):
+        return ds.transpose(*args, **kwargs)
+
+    for scale in list(multiscale_img.keys()):
+        assert multiscale_img[scale]["image"].dims == ("c", "y", "x")
+
+    # applying this function without skipping the root node would fail as the root node does not have dimensions.
+    result = multiscale_img.map_over_datasets(transpose, "y", "x", "c")
+    for scale in list(result.keys()):
+        assert result[scale]["image"].dims == ("y", "x", "c")