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  • dcherian · 3 ✖

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  • Time dtype encoding defaulting to `int64` when writing netcdf or zarr · 3 ✖

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  • MEMBER · 3 ✖
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965599998 https://github.com/pydata/xarray/issues/3942#issuecomment-965599998 https://api.github.com/repos/pydata/xarray/issues/3942 IC_kwDOAMm_X845jeL- dcherian 2448579 2021-11-10T18:01:46Z 2021-11-10T18:01:46Z MEMBER

Please may I ask: Why not default to xarray encoding time as 'units': 'nanoseconds since 1970-01-01' to be consistent with np.datetime64[ns]?

It's choosing the highest resolution that matches the data, which has the benefit of allowing the maximum possible time range given the data's frequency: https://github.com/pydata/xarray/blob/5871637873cd83c3a656ee6f4df86ea6628cf68a/xarray/coding/times.py#L317-L319

I'm not sure if this is why it was originally chosen; but that is one advantage. Perhaps @spencerkclark has some insight here.

 
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   Time dtype encoding defaulting to `int64` when writing netcdf or zarr 595492608
965591847 https://github.com/pydata/xarray/issues/3942#issuecomment-965591847 https://api.github.com/repos/pydata/xarray/issues/3942 IC_kwDOAMm_X845jcMn dcherian 2448579 2021-11-10T17:52:20Z 2021-11-10T17:52:20Z MEMBER

let's definitely add a note to the documentation to say that it might be a good idea for users to manually specify the encoding for datetimes if they wish to append to Zarrs.

:+1:

However I think xarray should raise an error when trying to append times that cannot be represented by the on-disk encoding.

Adding this error message would make it obvious that this is happening. PRs are very welcome!

 
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   Time dtype encoding defaulting to `int64` when writing netcdf or zarr 595492608
610429922 https://github.com/pydata/xarray/issues/3942#issuecomment-610429922 https://api.github.com/repos/pydata/xarray/issues/3942 MDEyOklzc3VlQ29tbWVudDYxMDQyOTkyMg== dcherian 2448579 2020-04-07T14:46:06Z 2020-04-07T14:46:06Z MEMBER

I have run in to this problem before.

The initial choice to use int64 and days since ... is perfectly valid. However I think xarray should raise an error when trying to append times that cannot be represented by the on-disk encoding.

Note that you can always specify an encoding to make sure that you can append properly.

 
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   Time dtype encoding defaulting to `int64` when writing netcdf or zarr 595492608

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