issue_comments: 383210788

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https://github.com/pydata/xarray/issues/2056#issuecomment-383210788 https://api.github.com/repos/pydata/xarray/issues/2056 383210788 MDEyOklzc3VlQ29tbWVudDM4MzIxMDc4OA== 5635139 2018-04-20T20:18:20Z 2018-04-20T20:18:20Z MEMBER

I'm happy to add this in.

A proposal, without a strong view: - When a dataset is supplied, a shallow copy of that dataset is returned - We raise if coords or attrs are passed. If you want those replaced, you can pass data_vars into the constructor. Otherwise I'm not sure how we'd have explicit behavior - We could add coords if they're not already there, but we'd need to either raise or silently replace if they were, which creates surprises - We could take the data_vars and attempt alignment, but if that's the desired behavior, you can pass the .data_vars

We could use this to take a decision on DataArray too. At the moment, coords are silently replaced: ``` xr.DataArray(xr.DataArray([1], coords={'a':[2222]}, dims=['a']), coords={'a':[2]}, dims=['a'])

<xarray.DataArray (a: 1)> array([1]) Coordinates: * a (a) int64 2 ```

I would suggest the same as above - people can pass .variable if they want to be able to pass coords.

I'm sure there's cases I haven't thought about - let me know any thoughts. CC @pydata/xarray 

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