issue_comments: 251715380

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https://github.com/pydata/xarray/pull/1038#issuecomment-251715380 https://api.github.com/repos/pydata/xarray/issues/1038 251715380 MDEyOklzc3VlQ29tbWVudDI1MTcxNTM4MA== 1217238 2016-10-05T15:50:06Z 2016-10-05T15:50:06Z MEMBER

I did some more digging and see some of the potential issues because some of the concatenation / merging is done quasi-automatically, which reduces the number of objects that must be merged (e.g., https://github.com/pydata/xarray/blob/master/xarray/core/combine.py#L391). I'm assuming this is done for performance / simplicity. Is that true?

We have two primitive combine operations, concat (same variables, different coordinate values) and merge (different variables, same coordinate values). auto_combine needs to do both in some order.

You're right that the order of grouped is not deterministic (it uses a dict). Sorting by key for input into the list comprehension could fix that.

The comprehensive fix would be to pick a merge strategy for attributes, and apply it uniformly in each place where xarray merges variables or datasets (basically, in concat and all the merge variations). Possibly several merge strategies, with a keyword argument to switch between them.

 
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