issues

Is your feature request related to a problem?

If we have two objects with dims x and x1, then xr.align(..., join="exact") will pass because these dimensions are broadcastable.

I'd like a stricter option (join="strict"?) that disallows broadcasting.

Describe the solution you'd like

python xr.align( xr.DataArray([1], dims="x"), xr.DataArray([1], dims="x1"), join="strict", ) would raise an error.

It'd be nice to have this as a built-in option so we can use python with xr.set_options(arithmetic_join="strict"): ...

Describe alternatives you've considered

An alternative would be to allow control over automatic broadcasting through the set_options context manager., but that seems like it would be more complicated to implement.

Additional context

This turns up in staggered grid calculations with xgcm where it is easy to mistakenly construct very high-dimensional arrays because of automatic broadcasting.

It'd be nice to issue a release soon. We should decide if this is a minor 0.15.2 or major 0.16.0

Please edit this list as you wish.

Must-have

• [x] #3936 multiple dims argmin, argmax

• [x] #4019, #4088; MultiIndex to sparse DataArray bug

• [x] #3922 fix dask array handling in idxmax, idxmin
• [x] #4009, #4173 combine_attrs with open_mfdataset
• [x] #3824 transpose coords (if major release)
• [x] #3926 remove old autocombine
• [x] #4135 nD dask arrays in idxmax/min

Nice to have

• [x] #4049, #4094 unstacking merge bug
• [ ] #4022 apply_ufunc meta vectorize
• [ ] #3924 interpolating to coordinates with nans
• [ ] #3925 sel along unindexed 1d coordinates
• [ ] #3993 replace dim with coord in integrate
• [ ] #3594 unit support with pint
• [ ] #4003 mfdataset with zarr
• [x] #3905 length of dataarray reprs
• [x] #3847 error summary for assert_allclose
• [x] #4033 infer_freq
• [x] #3938 plotting with multiindex
• [x] #3816 map_blocks template
• [x] #3976 in-place replacement error message
• [x] #3975 pint dataset
• [x] #4018 netdf3 dtype coercion
• [ ] #3985 groupby multi-index bug (ref discussion below & in the issue)

• [x] Closes #3575
• [x] Tests added
• [x] Passes isort -rc . && black . && mypy . && flake8
• [x] Fully documented, including whats-new.rst for all changes and api.rst for new API

This PR adds a template kwarg to map_blocks so that we can do more complicated things where automated inference of the template fails. template is expected to be an xarray object that looks like the result of the map_blocks computation.

@jhamman To me, this seems a lot easier than defining a dict based schema. With dask variables, the memory cost shouldn't be high. It's easy to use standard xarray operations to make something that looks like the result dataset. Here's a notebook prototyping a to_schema/from_schema approach: https://gist.github.com/dcherian/130ba22d0fbadb616837deb914eaa67e#file-map_blocks_for_metsim_test-ipynb

python ds = xr.tutorial.load_dataset("air_temperature").chunk({"lat": 5}) template = ds.isel(lat=slice(1, None, 5)) result = xr.map_blocks(lambda x: x.isel(lat=[1]), ds) # fails result = xr.map_blocks(lambda x: x.isel(lat=[1]), ds, template=template) # yay xr.testing.assert_equal(result, template) # passes Todo: - [x] add tests - [x] what if the function returns a variable not in the template? - [x] should we do anything with template.attrs?

Looks like our RTD builds have been failing for the last 3 days.

``` The HTML pages are in _build/html. /home/docs/checkouts/readthedocs.org/user_builds/xray/conda/latest/lib/python3.7/site-packages/sphinx_rtd_theme/search.html:20: RemovedInSphinx30Warning: To modify script_files in the theme is deprecated. Please insert a <script> tag directly in your theme instead. {{ super() }}

Traceback (most recent call last): File "/home/docs/checkouts/readthedocs.org/user_builds/xray/conda/latest/lib/python3.7/site-packages/sphinx/cmd/build.py", line 284, in build_main app.build(args.force_all, filenames) File "/home/docs/checkouts/readthedocs.org/user_builds/xray/conda/latest/lib/python3.7/site-packages/sphinx/application.py", line 380, in build self.events.emit('build-finished', None) File "/home/docs/checkouts/readthedocs.org/user_builds/xray/conda/latest/lib/python3.7/site-packages/sphinx/events.py", line 103, in emit results.append(callback(self.app, *args)) File "/home/docs/checkouts/readthedocs.org/user_builds/xray/conda/latest/lib/python3.7/site-packages/sphinx_gallery/gen_gallery.py", line 313, in sumarize_failing_examples "\n" + "-" * 79) ValueError: Here is a summary of the problems encountered when running the examples

Examples expected to fail, but not failing: Please remove these examples from sphinx_gallery_conf['expected_failing_examples'] /home/docs/checkouts/readthedocs.org/user_builds/xray/checkouts/latest/doc/gallery/plot_rasterio.pyin your conf.py file /home/docs/checkouts/readthedocs.org/user_builds/xray/checkouts/latest/doc/gallery/plot_rasterio_rgb.py

Exception occurred: File "/home/docs/checkouts/readthedocs.org/user_builds/xray/conda/latest/lib/python3.7/site-packages/sphinx_gallery/gen_gallery.py", line 313, in sumarize_failing_examples "\n" + "-" * 79) ValueError: Here is a summary of the problems encountered when running the examples

Examples expected to fail, but not failing: Please remove these examples from sphinx_gallery_conf['expected_failing_examples'] /home/docs/checkouts/readthedocs.org/user_builds/xray/checkouts/latest/doc/gallery/plot_rasterio.pyin your conf.py file /home/docs/checkouts/readthedocs.org/user_builds/xray/checkouts/latest/doc/gallery/plot_rasterio_rgb.py

```