issue_comments

The repr will be fixed by #5149, but we should probably still fix that. Since dim is the dimension to concatenate along I guess we should fall back to that (not sure though). Thoughts, @pydata/xarray?

For reference, the conversion happens in _calc_concat_dim_coord ("else"): https://github.com/pydata/xarray/blob/04acabb50bea9f48224464850ae5a918e57406e5/xarray/core/concat.py#L244-L265

Agree that this should coerce to the name of the dim if the array has no name.

Technically should the kwarg of concat be coord rather than dim? I generally supply dim names there, rather than coords vars. (though I'm not suggesting we actually change it given the backward-compat).

Note that we already do this in the DataArray constructor:

```python

In [12]: a = xr.DataArray([0,1], coords=[xr.DataArray([1,2])], dims='b') # No name on the coord

In [13]: a Out[13]: <xarray.DataArray (b: 2)> array([0, 1]) Coordinates: * b (b) int64 1 2 # Yes name on the coord ```

Thanks @keewis! I was confusing dimension names and variable names. I would support raising or falling back to a reasonably sane default -- the reason I stumbled on this was having a None coord name was breaking the _repr_html in Jupyter and causing a much more confusing error message

would've expected the name of the new coordinate to be the name of the DataArray variable

that's exactly what it's doing: it uses the name of DataArray([0, 1], dims='b'), which is None. To fix that, you can assign a name to the DataArray: python In [3]: a = xr.DataArray([0], dims='a') ...: out = xr.concat([a, a], dim=xr.DataArray([0, 1], dims='b', name="x")) ...: out Out[3]: <xarray.DataArray (b: 2, a: 1)> array([[0], [0]]) Coordinates: x (b) int64 0 1 Dimensions without coordinates: b, a

Since None is not a particularly good name, we could raise for unnamed DataArray objects (not sure if falling back to dims for 1D DataArray objects would be a good idea)