issue_comments: 630779096

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https://github.com/pydata/xarray/issues/4077#issuecomment-630779096 https://api.github.com/repos/pydata/xarray/issues/4077 630779096 MDEyOklzc3VlQ29tbWVudDYzMDc3OTA5Ng== 35968931 2020-05-19T12:14:41Z 2020-05-19T12:15:51Z MEMBER

Thanks for reporting this @malmans2!

There are actually two issues here: The minor one is that it should never have been possible to specify concat_dim and combine='by_coords' to open_mfdataset simultaneously. You should have got an error already at that point. xr.combine_by_coords doesn't accept a concat_dim argument, so neither should xr.open_mfdataset(..., combine='by_coords').

The more complex issue is that you can get the same overwriting problem in xr.combine_by_coords alone...

That was actually deliberate, xr.combine_by_coords is only checking the first value of each coord is different, to avoid loading big coordinates into memory. (see this line) As the first y value is 0 in both cases it's just saying "we have a match!" and overwriting.

@shoyer we discussed that PR (#2616) extensively, but I can't see an explicit record of discussing that particular line?

But since then @dcherian has done work on the options which vary the strictness of checking - should compat also vary this behaviour?

EDIT: (sorry for repeating what was said above, I wrote this reply last night and sent it today)

 
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