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/pull/5397#issuecomment-851721485,https://api.github.com/repos/pydata/xarray/issues/5397,851721485,MDEyOklzc3VlQ29tbWVudDg1MTcyMTQ4NQ==,14808389,2021-05-31T23:58:54Z,2021-05-31T23:58:54Z,MEMBER,"> keeping the full list in memory isn't expensive at all IIUC

I agree, this should not be an issue at all: we're iterating over `datasets` multiple times so we definitely need it to be a sequence (currently it's some kind of iterator object, e.g. the one returned by `dict.keys`).","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,905848466
https://github.com/pydata/xarray/pull/5397#issuecomment-851624047,https://api.github.com/repos/pydata/xarray/issues/5397,851624047,MDEyOklzc3VlQ29tbWVudDg1MTYyNDA0Nw==,5635139,2021-05-31T18:15:20Z,2021-05-31T18:15:20Z,MEMBER,"> Will it not cripple performance due to the non-lazy evaluation of the list ?

I don't think so, but I'm not sure — keeping the full list in memory isn't expensive at all IIUC. And either way, it'll confirm the reason for the test failures for now.


> I also started the test for the concat function, I discovered that if the first element determine between `_dataarray_concat` and `_dataset_concat`. I am not sure if I need to do several commits (type checking dataset, type checking data array) and several test.
> 
> Here is the draft for the tests:
> 

Those look good! Feel free to add them directly and we can discuss them there, and see the test results. Thanks!","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,905848466
https://github.com/pydata/xarray/pull/5397#issuecomment-851618811,https://api.github.com/repos/pydata/xarray/issues/5397,851618811,MDEyOklzc3VlQ29tbWVudDg1MTYxODgxMQ==,37740986,2021-05-31T17:59:46Z,2021-05-31T17:59:46Z,CONTRIBUTOR,"Will it not cripple performance due to the non-lazy evaluation of the list ?

I also started the test for the concat function, I discovered that if the first element determine between `_dataarray_concat` and `_dataset_concat`. I am not sure if I need to do several commits (type checking dataset, type checking data array) and several test.

Here is the draft for the tests:
```
def test_concat_check_input_type():
    ds = Dataset({""foo"": 1}, {""bar"": 2})
    da = Dataset({""foo"": 3}, {""bar"": 4}).to_array(dim='foo')

    # concatenate a list of non-homogeneous types must raise TypeError
    with pytest.raises(TypeError, match=""Some elements in the input list datasets are not 'DataSet'""):
        concat([ds, da], dim=""foo"")

    # concatenate a list of non-homogeneous types must raise TypeError
    with pytest.raises(TypeError, match=""Some elements in the input list datasets are not 'DataArray'""):
        concat([da, ds], dim=""foo"")
```

Code I plan to add also for the typing check in `_dataarray_concat`:
```
    from .dataarray import DataArray
    arrays = list(arrays)
    if not all(isinstance(array, DataArray) for array in list(arrays)):
        raise TypeError(""Some elements in the input list datasets are not 'DataArray'"")
```
(I need to add `from .dataarray import DataArray` to be able to use the type)
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,905848466
https://github.com/pydata/xarray/pull/5397#issuecomment-850666780,https://api.github.com/repos/pydata/xarray/issues/5397,850666780,MDEyOklzc3VlQ29tbWVudDg1MDY2Njc4MA==,37740986,2021-05-28T20:58:53Z,2021-05-28T20:58:53Z,CONTRIBUTOR,"Ok! I'll do that in the next few days :)
I'm trying to get more familiar with the whole procedure","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,905848466
https://github.com/pydata/xarray/pull/5397#issuecomment-850662147,https://api.github.com/repos/pydata/xarray/issues/5397,850662147,MDEyOklzc3VlQ29tbWVudDg1MDY2MjE0Nw==,5635139,2021-05-28T20:47:48Z,2021-05-28T20:47:48Z,MEMBER,"Hi @thomashirtz ! Thanks for the PR.

The code looks reasonable, though it's generating test failures. To prioritize giving quick feedback over complete feedback — possibly `datasets` is sometimes a generator. We could add `datasets = list(datasets)` above the current code. If that doesn't fix it, feel free to take an error and try debugging what's going on, or someone can help.

We should add a test for this too.
","{""total_count"": 1, ""+1"": 1, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,905848466