issue_comments: 489236748

This data as json

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/1849#issuecomment-489236748 https://api.github.com/repos/pydata/xarray/issues/1849 489236748 MDEyOklzc3VlQ29tbWVudDQ4OTIzNjc0OA== 12465248 2019-05-03T20:54:50Z 2019-05-03T20:54:50Z CONTRIBUTOR

@dcherian Thanks,

First, I think you're right that the encoding['contiguous']=True is coming from the input file. That was not clear to me (and I did not read the xarray code to verify). But it makes sense.

Second, my example shows something more slightly complicated than the original example which was also not clear to me. In my case the unlimited dimension (time) is chunked and is being successfully written in both cases (before and after work around). The error/ failure is happening on the a variable that contains the unlimited dimension but which has encoding['contiguous']=True for the variable.

This makes sense upon a slightly more nuanced reading of the netcdf4 manual (as quoted my markelg)

"contiguous: if True (default False), the variable data is stored contiguously on disk. Default False. Setting to True for a variable with an unlimited dimension will trigger an error."

The last sentence apparently means that for any variable with an unlimited dimension the use of contiguous=True triggers an error. That was not clear to me until I looked a bit harder at this. I think that slightly refines the strategy of how to deal with the problem.

I propose that the solution should be both a) delete encoding['contiguous'] if it is True when asked to write out a variable containing an unlimited dimension. b) raise an informative warning that the variable was chunked because it contained an unlimited dimension. (If a user hates warnings, they could can handle this deletion herself. One the other hand, there's really nothing else to do, so I'm not sure the warning is necessary... I dont have strong opinion on this, but the code is fiddling with the encodings under the hood, so a warning seems polite).

A final question: should the encoding['contiguous'] be removed from the xarray variable or should it just be removed for purposes of writing it to ncdf4 on disk? I suppose a user could be writing the xarray dataset to another format that might allow what netcdf does not allow. This should be an easy detail.

I'll make a PR with the above and we can evaluate the concrete changes.

 
{
    "total_count": 0,
    "+1": 0,
    "-1": 0,
    "laugh": 0,
    "hooray": 0,
    "confused": 0,
    "heart": 0,
    "rocket": 0,
    "eyes": 0
}
   290572700