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/2647#issuecomment-451746014,https://api.github.com/repos/pydata/xarray/issues/2647,451746014,MDEyOklzc3VlQ29tbWVudDQ1MTc0NjAxNA==,35968931,2019-01-06T14:32:08Z,2019-01-06T14:32:08Z,MEMBER,"I just wanted to clarify that `concat_dim=None` very much does mean something special, it means ""don't use `concat` on these datasets at all, just use `merge`"". This is documented under the `concat_dim` argument description of the docs for `auto_combine` [here](http://xarray.pydata.org/en/stable/generated/xarray.auto_combine.html#xarray.auto_combine). 

Also @WeatherGod I think this bug was introduced by me in #2553, but should be checked again once #2616 is finished, because the API will change.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,395994055
https://github.com/pydata/xarray/issues/2647#issuecomment-451504997,https://api.github.com/repos/pydata/xarray/issues/2647,451504997,MDEyOklzc3VlQ29tbWVudDQ1MTUwNDk5Nw==,291576,2019-01-04T17:06:50Z,2019-01-04T17:06:50Z,CONTRIBUTOR,"scratch that... the test was an `or`, not a `and`.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,395994055
https://github.com/pydata/xarray/issues/2647#issuecomment-451504888,https://api.github.com/repos/pydata/xarray/issues/2647,451504888,MDEyOklzc3VlQ29tbWVudDQ1MTUwNDg4OA==,1217238,2019-01-04T17:06:30Z,2019-01-04T17:06:30Z,MEMBER,"I think `concat_dim=None` may mean something special here, which is why we have `_CONCAT_DIM_DEFAULT`","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,395994055
https://github.com/pydata/xarray/issues/2647#issuecomment-451504462,https://api.github.com/repos/pydata/xarray/issues/2647,451504462,MDEyOklzc3VlQ29tbWVudDQ1MTUwNDQ2Mg==,291576,2019-01-04T17:05:00Z,2019-01-04T17:05:00Z,CONTRIBUTOR,"actually, we could simplify the conditional to be just `concat_dim is _CONCAT_DIM_DEFAULT` and not bother with the `None` test.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,395994055
https://github.com/pydata/xarray/issues/2647#issuecomment-451504141,https://api.github.com/repos/pydata/xarray/issues/2647,451504141,MDEyOklzc3VlQ29tbWVudDQ1MTUwNDE0MQ==,291576,2019-01-04T17:03:54Z,2019-01-04T17:03:54Z,CONTRIBUTOR,ah! that's why it snuck through! I have been raking my brain on this for the past hour! shall I go ahead and make a PR?,"{""total_count"": 1, ""+1"": 1, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,395994055
https://github.com/pydata/xarray/issues/2647#issuecomment-451502294,https://api.github.com/repos/pydata/xarray/issues/2647,451502294,MDEyOklzc3VlQ29tbWVudDQ1MTUwMjI5NA==,1217238,2019-01-04T16:57:33Z,2019-01-04T16:57:33Z,MEMBER,"Indeed, this is should definitely be `concat_dim is _CONCAT_DIM_DEFAULT` for comparing to a sentinel value.

I think this snuck through because NumPy will automatically cast size 1 arrays (of any shape) to booleans :(. We should probably adapt that test to include an explicit dimension of size greater than 1.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,395994055
https://github.com/pydata/xarray/issues/2647#issuecomment-451501740,https://api.github.com/repos/pydata/xarray/issues/2647,451501740,MDEyOklzc3VlQ29tbWVudDQ1MTUwMTc0MA==,291576,2019-01-04T16:55:40Z,2019-01-04T16:55:40Z,CONTRIBUTOR,"To be more explicit, the issue is that `concat_dim == _CONCAT_DIM_DEFAULT` is ill-advised because the type of `concat_dim` is not guaranteed to be a scalar. In fact, the elif of that area of code in api.py explicitly tests if concat_dim is or is not a list.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,395994055