id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
403378297,MDU6SXNzdWU0MDMzNzgyOTc=,2714,Extra dimension on first argument passed into apply_ufunc,1796208,open,0,,,13,2019-01-26T00:04:47Z,2022-05-06T03:03:00Z,,NONE,,,,"Here's my code:

```python
import numpy as np
import xarray as xr

da = xr.DataArray(np.random.rand(1000, 100))
da = da.rename({'dim_0': 'rows_a'})
db = xr.DataArray(np.random.rand(1000, 100))
db = db.rename({'dim_0': 'rows_b'})

def print_shape(a):
    print(a.shape)
    return np.zeros(shape=(a.shape[0]))

def print_two_shapes(a, b):
    print(a.shape)
    print(b.shape)
    return np.zeros(shape=(a.shape[0], b.shape[0]))
```

If I print_shape and print_shapes with apply_ufunc I am surprised by the results:

```python
xr.apply_ufunc(
    print_shape,
    da,
    input_core_dims=[['dim_1']]
)

(1000, 100)
<xarray.DataArray (rows_a: 1000)>
array([0., 0., 0., ..., 0., 0., 0.])
Coordinates:
  * rows_a   (rows_a) int64 0 1 2 3 4 5 6 7 ... 992 993 994 995 996 997 998 999
```

vs

```python
xr.apply_ufunc(
    print_two_shapes,
    da, db,
    input_core_dims=[['dim_1'], ['dim_1']]
)

(1000, 1, 100)
(1000, 100)

<xarray.DataArray (rows_a: 1000, rows_b: 1000)>
array([[0., 0., 0., ..., 0., 0., 0.],
       [0., 0., 0., ..., 0., 0., 0.],
       [0., 0., 0., ..., 0., 0., 0.],
       ...,
       [0., 0., 0., ..., 0., 0., 0.],
       [0., 0., 0., ..., 0., 0., 0.],
       [0., 0., 0., ..., 0., 0., 0.]])
Coordinates:
  * rows_a   (rows_a) int64 0 1 2 3 4 5 6 7 ... 992 993 994 995 996 997 998 999
  * rows_b   (rows_b) int64 0 1 2 3 4 5 6 7 ... 992 993 994 995 996 997 998 999
```

My array `da` has changed shape from `(1000, 100)` to `(1000, 1, 100)` when a second argument was added to my call to `apply_ufunc`.

Maybe this is documented, but I missed it. If it is documented I'd be glad to be pointed to it and I'll see if I can come up with a suggestion of how to highlight this better in the documentation as it really threw me.","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/2714/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,issue