id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type 893692903,MDU6SXNzdWU4OTM2OTI5MDM=,5326,map_blocks doesn't handle tranposed arrays,20629530,closed,0,,,7,2021-05-17T20:34:58Z,2021-05-18T14:14:37Z,2021-05-18T14:14:37Z,CONTRIBUTOR,,,," **What happened**: I was using `map_blocks` for a complex function which returns an array with a different dimension order than the input. Because of the complexity of the wrapped func, I need to generate a `template` first. When calling `map_blocks` and loading the result, it passes all checks in `map_blocks` but `Variable` fails when assigning the new data. **What you expected to happen**: I expected no failure. Either the result would have transposed dimensions, or it would have been transposed back to fit with `template`. **Minimal Complete Verifiable Example**: ```python import xarray as xr da = xr.DataArray([[0, 1, 2], [3, 4, 5]], dims=('x', 'y')) def func(d): return d.transpose() dac = da.chunk() dac.map_blocks(func, template=dac).load() ``` Traceback: ```python --------------------------------------------------------------------------- ValueError Traceback (most recent call last) in 7 8 dac = da.chunk() ----> 9 dac.map_blocks(func, template=dac).load() ~/.conda/envs/xclim/lib/python3.8/site-packages/xarray/core/dataarray.py in load(self, **kwargs) 871 dask.compute 872 """""" --> 873 ds = self._to_temp_dataset().load(**kwargs) 874 new = self._from_temp_dataset(ds) 875 self._variable = new._variable ~/.conda/envs/xclim/lib/python3.8/site-packages/xarray/core/dataset.py in load(self, **kwargs) 799 800 for k, data in zip(lazy_data, evaluated_data): --> 801 self.variables[k].data = data 802 803 # load everything else sequentially ~/.conda/envs/xclim/lib/python3.8/site-packages/xarray/core/variable.py in data(self, data) 378 data = as_compatible_data(data) 379 if data.shape != self.shape: --> 380 raise ValueError( 381 f""replacement data must match the Variable's shape. "" 382 f""replacement data has shape {data.shape}; Variable has shape {self.shape}"" ValueError: replacement data must match the Variable's shape. replacement data has shape (3, 2); Variable has shape (2, 3) ``` If `func` is made to return `d` (no transpose), the code works. I actually not sure which behaviour would be the best : a result with transposed dimensions to fit with the wrapped func or to tranpose the result to fit with the template. The latter seems much easier to implement by editing `core/parallel.py` and add the transposition at the end of `_wrapper()` in `map_blocks()`. **Environment**:
Output of xr.show_versions() INSTALLED VERSIONS ------------------ commit: None python: 3.8.8 | packaged by conda-forge | (default, Feb 20 2021, 16:22:27) [GCC 9.3.0] python-bits: 64 OS: Linux OS-release: 5.11.16-arch1-1 machine: x86_64 processor: byteorder: little LC_ALL: None LANG: fr_CA.utf8 LOCALE: ('fr_CA', 'UTF-8') libhdf5: 1.10.6 libnetcdf: 4.7.4 xarray: 0.17.1.dev99+gc58e2aeb.d20210430 pandas: 1.2.4 numpy: 1.20.2 scipy: 1.6.3 netCDF4: 1.5.6 pydap: installed h5netcdf: 0.11.0 h5py: 3.2.1 Nio: None zarr: 2.8.1 cftime: 1.4.1 nc_time_axis: 1.2.0 PseudoNetCDF: installed rasterio: 1.2.2 cfgrib: 0.9.9.0 iris: 2.4.0 bottleneck: 1.3.2 dask: 2021.04.0 distributed: 2021.04.1 matplotlib: 3.4.1 cartopy: 0.19.0 seaborn: 0.11.1 numbagg: installed pint: 0.17 setuptools: 49.6.0.post20210108 pip: 21.1 conda: None pytest: 6.2.3 IPython: 7.22.0 sphinx: 3.5.4
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