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  • keewis · 2 ✖

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  • `xr.where()` does not work like `np.where()`on meshgrids · 2 ✖

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883232093 https://github.com/pydata/xarray/issues/5620#issuecomment-883232093 https://api.github.com/repos/pydata/xarray/issues/5620 IC_kwDOAMm_X840pQ1d keewis 14808389 2021-07-20T09:09:31Z 2021-07-20T09:44:42Z MEMBER

Actually, I can reproduce this with the example "rasm" dataset: python In [2]: import xarray as xr ...: ...: rasm = xr.tutorial.open_dataset("rasm").load() ...: ...: min_lat = 17 ...: max_lat = 18 ...: min_lon = 189 ...: max_lon = 190 ...: ...: mask = ( ...: (rasm.xc <= max_lon) & (rasm.xc > min_lon) ...: & (rasm.yc <= max_lat) & (rasm.yc > min_lat) ...: ) ...: ...: subset = rasm.xc.where(mask, drop=True) ...: display(subset.max(), subset.xc.max()) ...: display(subset, subset.xc) <xarray.DataArray 'xc' ()> array(189.89982737) <xarray.DataArray 'xc' ()> array(190.07286203) <xarray.DataArray 'xc' (y: 3, x: 4)> array([[189.55836619, 189.72833384, 189.89982737, nan], [189.30253733, 189.47184886, 189.64270151, 189.81509531], [189.04515208, 189.21383799, 189.38403452, nan]]) Coordinates: xc (y, x) float64 189.6 189.7 189.9 190.1 ... 189.0 189.2 189.4 189.6 yc (y, x) float64 17.02 17.27 17.51 17.76 ... 17.34 17.59 17.84 18.08 Dimensions without coordinates: y, x Attributes: long_name: longitude of grid cell center units: degrees_east <xarray.DataArray 'xc' (y: 3, x: 4)> array([[189.55836619, 189.72833384, 189.89982737, 190.07286203], [189.30253733, 189.47184886, 189.64270151, 189.81509531], [189.04515208, 189.21383799, 189.38403452, 189.55578745]]) Coordinates: xc (y, x) float64 189.6 189.7 189.9 190.1 ... 189.0 189.2 189.4 189.6 yc (y, x) float64 17.02 17.27 17.51 17.76 ... 17.34 17.59 17.84 18.08 Dimensions without coordinates: y, x Attributes: long_name: longitude of grid cell center units: degrees_east

which makes it pretty obvious why this fails: drop=True drops as much as possible, but to really drop everything we would have to collapse the result to 1D. To work around that, .where sets the data to nan where necessary, but only for data variables (as coordinates still need to label the masked values).

 
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   `xr.where()` does not work like `np.where()`on meshgrids 947796627
883226384 https://github.com/pydata/xarray/issues/5620#issuecomment-883226384 https://api.github.com/repos/pydata/xarray/issues/5620 IC_kwDOAMm_X840pPcQ keewis 14808389 2021-07-20T09:01:34Z 2021-07-20T09:01:34Z MEMBER

@meteoDaniel, it ultimately comes down to how much time a maintainer is willing to spend on a single issue, with self-contained, small examples being much easier to debug (and there are a few other reasons in the blog post linked to by @max-sixty).

That said, I can reproduce your issue, which apparently is independent of the way the mask is constructed: ```python mask = ( (latitudes <= maxLat) & (latitudes > minLat) & (longitudes <= maxLon) & (longitudes > minLon) )

ds.where(xr.DataArray(mask, dims=("y", "x")), drop=True).latitude.max() # 49.30 latitudes[mask].max() # 48.92 ```

However, if I do python subset = ds.latitude.where(xr.DataArray(mask, dims=("y", "x")), drop=True) subset.max() I get the same result as with pure numpy.

Interestingly, xr.testing.assert_identical(subset, subset.latitude) raises...

 
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   `xr.where()` does not work like `np.where()`on meshgrids 947796627

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