html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/2180#issuecomment-391932929,https://api.github.com/repos/pydata/xarray/issues/2180,391932929,MDEyOklzc3VlQ29tbWVudDM5MTkzMjkyOQ==,1217238,2018-05-25T03:46:40Z,2018-05-25T03:46:40Z,MEMBER,"Looking at @crusaderky's example of different coordinate labels again, I finally remember why it works this way.

The logic of `ds.update(other)` is that (1) variables explicitly listed in `other` should take precedence over the original object and (2) mutating a Dataset should not change its dimensions or indexes.

This is pretty clearly expressed in the original code:
```
    return merge_core([dataset, other], priority_arg=1,
                      indexes=dataset.indexes)
```

In @crusaderky's example with `fridge.update(shopping)`, `shopping` first gets reindexed to `fridge` (which means it ends up only holding NaN), and is then used to override the original dataset:
```
<xarray.Dataset>
Dimensions:  (fruit: 1)
Coordinates:
  * fruit    (fruit) object 'apples'
    quality  (fruit) object nan
Data variables:
    fruits   (fruit) float64 nan
```
It would probably make sense to keep values from the original variables rather than blindly replacing them with the new NaNs from `shopping`, but in general I do think the general approach of ""right join on variables"" and ""left join on indexes"" makes sense for `update()`.

For most use cases, the true outer join makes more sense -- which is why `xarray.merge()` works that way.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,326205036
https://github.com/pydata/xarray/issues/2180#issuecomment-391908821,https://api.github.com/repos/pydata/xarray/issues/2180,391908821,MDEyOklzc3VlQ29tbWVudDM5MTkwODgyMQ==,1217238,2018-05-25T00:50:58Z,2018-05-25T00:51:10Z,MEMBER,@crusaderky this behavior you show is indeed really strange. I don't know why alignment of dimensions works that way currently.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,326205036
https://github.com/pydata/xarray/issues/2180#issuecomment-391908588,https://api.github.com/repos/pydata/xarray/issues/2180,391908588,MDEyOklzc3VlQ29tbWVudDM5MTkwODU4OA==,1217238,2018-05-25T00:49:15Z,2018-05-25T00:49:15Z,MEMBER,"OK, looking at this more carefully `ds.update(other)` didn't actually change when other is a `Dataset`, because `ds[k] = ds[k].drop(coord_names)` doesn't actually drop coordinates from a Dataset. It just shows a warning now, due to iteration over a Dataset.

So maybe we can leave the current behavior as is for now (but remove the warning).

What did change is how we handle conflicts in `__setitem__` (which was intentional), and how we handle conflicts in `update` when the new value is a dictionary (which was *not* intentional, but at least remained consistent with `__setitem__`).","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,326205036
https://github.com/pydata/xarray/issues/2180#issuecomment-391898293,https://api.github.com/repos/pydata/xarray/issues/2180,391898293,MDEyOklzc3VlQ29tbWVudDM5MTg5ODI5Mw==,1217238,2018-05-24T23:40:34Z,2018-05-24T23:40:41Z,MEMBER,cc @fujiisoup @crusaderky ,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,326205036