issue_comments: 1234639080

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https://github.com/pydata/xarray/issues/3731#issuecomment-1234639080 https://api.github.com/repos/pydata/xarray/issues/3731 1234639080 IC_kwDOAMm_X85Jlxjo 3698640 2022-09-01T18:31:08Z 2022-09-01T18:31:08Z CONTRIBUTOR

ooh this is a fun one! came across this issue when we stumbled across a pendantic case writing tests (H/T @brews). I expected this to "fail loudly in the constructor" but it doesn't. note that currently AFAICT you cannot use positional slicing to achieve an intuitive result - the behavior seems more undefined/unpredictable

```python

setup

import xarray as xr, pandas as pd, numpy as np da = xr.DataArray(np.arange(8).reshape(2, 2, 2), coords=[[0, 1], [0, 1], ['a', 'b']], dims=["ni", "ni", "shh"]) xarray seems to not know it has a problem:python In [4]: da Out[4]: <xarray.DataArray (ni: 2, shh: 2)> array([[[0, 1], [2, 3]],

   [[4, 5],
    [6, 7]]])

Coordinates: * ni (ni) int64 0 1 * shh (shh) <U1 'a' 'b' slicing (somewhat intuitively? slices along both dims):python In [5]: da.sel(ni=0) Out[5]: <xarray.DataArray (shh: 2)> array([0, 1]) Coordinates: ni int64 0 * shh (shh) <U1 'a' 'b' however, positional slicing (and any attempts I've made to handle the repeated dims differently) seems to have undefined behavior:python In [6]: da[0, :, :] # positional slicing along first dim works as expected(?) Out[6]: <xarray.DataArray (ni: 2, shh: 2)> array([[[0, 1], [2, 3]],

   [[4, 5],
    [6, 7]]])

Coordinates: * ni (ni) int64 0 1 * shh (shh) <U1 'a' 'b'

In [7]: da[:, 0, :] # positional slicing along second dim slices both dims Out[7]: <xarray.DataArray (shh: 2)> array([0, 1]) Coordinates: ni int64 0 * shh (shh) <U1 'a' 'b' ```

 
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