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I think this will share a similar API with the evenly spaced coordinate discussed in issue #1650.

I thought the possible API would be xr.Dataset({'foo': ('x', data)}, {'x': slice(None)}) where it will construct a evenly spaced coordinate. But I am not sure if we should add this API now or after #1650 is implemented.

My issue is not so much with the range but the len. If done during construction from numpy arrays, it might need to be range(data.shape[0]) or range(data.shape[1]) or etc. based on the layout of the data. If done after construction with assign_coords, both the name of the dataset and the name of the dimension need to be written twice. This all creates room for silly mistakes.

On the bright side, the mistakes are quickly caught when the code executes at runtime. On the other side, they can be entirely avoided.

Of course, xarray doesn't have to do this; a user concerned about making these mistakes can easily capture this usage pattern in a wrapper function around assign_coords:

python def assign_auto_coords(da, *dims): """Give each specified dimension of a DataArray or Dataset automatic coords from 0 to n-1.""" return da.assign_coords(**{dim: range(self.sizes[dim]) for dim in dims})

it's merely that first-class support during construction would be nice to have.

If I understand correctly, instead of writing xr.Dataset({'foo': ('x', data)}, {'x': range(len(data))}), you want to be able to write something like xr.Dataset({'foo': ('x', data)}, {'x': xr.AUTO_NUMBER})?

I agree that it's sometimes convenient to automatically get coordinates 0 to n-1, but using range() is also pretty convenient, so I'm not sure we really need this shortcut.