issue_comments

We could also make it only succeed if DataArray.name is None and raise an error otherwise.

Supporting the tuple form also seems like a good idea

One option here would be to take the name of the dataarray iff the dim name is dim_0. While I'm not a great fan of breaking that abstraction and hardcoding exceptions, it does solve the case quite well:

```python

In [7]: xr.concat([da,da], xr.DataArray(['x', 'y'], name='stat')) Out[7]: <xarray.DataArray 'air' (dim_0: 2, time: 2920, lat: 25, lon: 53)> array([[[[241.2 , 242.5 , 243.5 , ..., 232.79999, 235.5 , 238.59999], [243.79999, 244.5 , 244.7 , ..., 232.79999, 235.29999, 295.19 ], [297.69 , 298.09 , 298.09 , ..., 296.49 , 296.19 , 295.69 ]]]], dtype=float32) Coordinates: * lat (lat) float32 75.0 72.5 70.0 67.5 65.0 ... 25.0 22.5 20.0 17.5 15.0 * lon (lon) float32 200.0 202.5 205.0 207.5 ... 322.5 325.0 327.5 330.0 * time (time) datetime64[ns] 2013-01-01 ... 2014-12-31T18:00:00 * dim_0 (dim_0) <U1 'x' 'y' # Very unlikely we even want dim_0 here ```

It's very unlikely we even want dim_0 there rather than stat

What is the desired behaviour in this case viz. do we preserve dimension name new_dim or assign new name stat?

Oh, this is trickier than I thought!

The challenge is that once you make the DataArray, there is no good way to know if a default dimension name like 'dim_0' was intentional or not.

The way to handle this currently is to pass a 1-dimensional xarray.Variable object for the dim argument. These don't have separate names, so there's no ambiguity: In [5]: xarray.concat([xarray.DataArray(1), xarray.DataArray(2)], dim=xarray.Variable('x', [3, 4])) Out[5]: <xarray.DataArray (x: 2)> array([1, 2]) Coordinates: * x (x) int64 3 4

But this is a little verbose. Potentially we could call xarray.as_variable() on tuple inputs (like in the Dataset constructor) so dim=('x', [3, 4]) works.

I have a simple fix in #1812 .

With that change, this works.

print(xarray.concat(data, xarray.DataArray(['foo1', 'foo2', 'foo3', 'foo4', 'foo5'], name='stat'))

But if you provided a dimension name like

print(xarray.concat(data, xarray.DataArray(['foo1', 'foo2', 'foo3', 'foo4', 'foo5'], dims=['new_dim'], name='stat'))

then new_dim is renamed to stat. What is the desired behaviour in this case viz. do we preserve dimension name new_dim or assign new name stat?

This is the location of the helper function that parsing the dim argument: https://github.com/pydata/xarray/blob/9763a66e0e4675e7adc3fff3830c62f0e31a2bb3/xarray/core/combine.py#L123

Agreed, this should definitely work! (I think the fact that it doesn't is probably related to the relatively recent change that made coordinate labels along dimensions optional.)