issues: 388901771

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
388901771 MDU6SXNzdWUzODg5MDE3NzE= 2594 When use groupby to convert monthly array into yearly array by mean (dim=time), does xr consider the weights of each month or just take average? 19677300 closed 0     1 2018-12-08T08:44:30Z 2019-01-04T01:01:34Z 2019-01-04T01:01:34Z NONE      

Code Sample, a copy-pastable example if possible

A "Minimal, Complete and Verifiable Example" will make it much easier for maintainers to help you: http://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports

```python

Your code here

```

Problem description

[this should explain why the current behavior is a problem and why the expected output is a better solution.]

Expected Output

Output of xr.show_versions()

# Paste the output here xr.show_versions() here 
{
    "url": "https://api.github.com/repos/pydata/xarray/issues/2594/reactions",
    "total_count": 0,
    "+1": 0,
    "-1": 0,
    "laugh": 0,
    "hooray": 0,
    "confused": 0,
    "heart": 0,
    "rocket": 0,
    "eyes": 0
}
   completed 13221727 issue

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