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/2968#issuecomment-493453581,https://api.github.com/repos/pydata/xarray/issues/2968,493453581,MDEyOklzc3VlQ29tbWVudDQ5MzQ1MzU4MQ==,10194086,2019-05-17T13:28:29Z,2019-05-17T13:28:29Z,MEMBER,"I think you can keep the function signature of `reduce` but rather allow to set  `min_periods=0` in `__init__` (This is currently disallowed on [Line 77](https://github.com/pydata/xarray/blob/master/xarray/core/rolling.py#L77)). 

Then you change your code in `reduce` to
``` python
if self.min_periods == 0:
    return result

```

btw: If I understand correctly, this does not need to be added for the other functions `ds.rolling(...).mean()` calls `reduce` on [Line 238](https://github.com/pydata/xarray/blob/master/xarray/core/rolling.py#L238).","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,445045305