issues: 788534915

This data as json

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
788534915 MDU6SXNzdWU3ODg1MzQ5MTU= 4824 combine_by_coords can succed when it shouldn't 10194086 open 0     15 2021-01-18T20:39:29Z 2021-07-08T17:44:38Z   MEMBER      

What happened:

combine_by_coords can succeed when it should not - depending on the name of the dimensions (which determines the order of operations in combine_by_coords).

What you expected to happen:

  • I think it should throw an error in both cases.

Minimal Complete Verifiable Example:

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

data = np.arange(5).reshape(1, 5) x = np.arange(5) x_name = "lat"

da0 = xr.DataArray(data, dims=("t", x_name), coords={"t": [1], x_name: x}).to_dataset(name="a") x = x + 1e-6 da1 = xr.DataArray(data, dims=("t", x_name), coords={"t": [2], x_name: x}).to_dataset(name="a") ds = xr.combine_by_coords((da0, da1))

ds ```

returns: python <xarray.Dataset> Dimensions: (lat: 10, t: 2) Coordinates: * lat (lat) float64 0.0 1e-06 1.0 1.0 2.0 2.0 3.0 3.0 4.0 4.0 * t (t) int64 1 2 Data variables: a (t, lat) float64 0.0 nan 1.0 nan 2.0 nan ... 2.0 nan 3.0 nan 4.0 Thus lat is interlaced - it don't think combine_by_coords should do this. If you set

python x_name = "lat" and run the example again, it returns:

```python-traceback ValueError: Resulting object does not have monotonic global indexes along dimension x

```

Anything else we need to know?:

  • this is vaguely related to #4077 but I think it is separate
  • combine_by_coords concatenates over all dimensions where the coords are different - therefore compat="override" doesn't actually do anything? Or does it?

https://github.com/pydata/xarray/blob/ba42c08af9afbd9e79d47bda404bf4a92a7314a0/xarray/core/combine.py#L69

cc @dcherian @TomNicholas

Environment:

Output of <tt>xr.show_versions()</tt> 
{
    "url": "https://api.github.com/repos/pydata/xarray/issues/4824/reactions",
    "total_count": 0,
    "+1": 0,
    "-1": 0,
    "laugh": 0,
    "hooray": 0,
    "confused": 0,
    "heart": 0,
    "rocket": 0,
    "eyes": 0
}
     13221727 issue

Links from other tables