Stack xarray DataArray

Question

I have N 1D xr.DataArray 's with an 1 array coordinate b and 1 scalar coordinate a . I want to combine them to a 2D DataArray with array coordinates b , a . How to do this? I have tried:

x1 = xr.DataArray(np.arange(0,3)[...,np.newaxis], coords=[('b', np.arange(3,6)),('a', [10])]).squeeze()
x2 = xr.DataArray(np.arange(0,3)[...,np.newaxis], coords=[('b', np.arange(3,6)),('a', [11])]).squeeze()

xcombined = xr.concat([x1, x2])
xcombined

Results in :

<xarray.DataArray (concat_dims: 2, b: 3)>
array([[0, 1, 2],
       [0, 1, 2]])
Coordinates:
  * b        (b) int64 3 4 5
    a        (concat_dims) int64 10 11
Dimensions without coordinates: concat_dims

Now I like to select a particularly 'a':

xcombined.sel(a=10)

However, this raises:

ValueError: dimensions or multi-index levels ['a'] do not exist

Answer 1

If you supply dim to concat , this works:

xcombined = xr.concat([x1, x2], dim='a')

And then:

xcombined.sel(a=10)

<xarray.DataArray (b: 3)>
array([0, 1, 2])
Coordinates:
  * b        (b) int64 3 4 5
    a        int64 10