html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/722#issuecomment-176884522,https://api.github.com/repos/pydata/xarray/issues/722,176884522,MDEyOklzc3VlQ29tbWVudDE3Njg4NDUyMg==,242610,2016-01-29T17:48:15Z,2016-01-29T17:48:15Z,NONE,"Thank you!

I was just wondering how you know then, which one is an ""actual"" coordinate and which one is an indexed (""default"") coordinate?

xarray seem to know this.

Example:

```
In [1]: import xray as xr

In [2]: import numpy as np

In [3]: var1 = xr.DataArray(np.array([1, 2], np.float64), coords=[np.array([1, 2], np.int64)], dims=[""coor1"",], name = ""var1"")

In [4]: var2 = xr.DataArray(np.array([3, 4], np.float64), dims=[""dim1"",], name = ""var2"")

In [5]: ds.var1
Out[5]: 
<xray.DataArray 'var1' (coor1: 2)>
array([ 1.,  2.])
Coordinates:
  * coor1    (coor1) int64 1 2

In [6]: ds.var2
Out[6]: 
<xray.DataArray 'var2' (dim1: 2)>
array([ 3.,  4.])
Coordinates:
  * dim1     (dim1) int64 0 1

In [7]: ds.var1.coords
Out[7]: 
Coordinates:
  * coor1    (coor1) int64 1 2

In [8]: ds.var2.coords
Out[8]: 
Coordinates:
  * dim1     (dim1) int64 0 1

In [9]: ds.to_netcdf(""/tmp/from_xr.nc"")
```

And then

```
$ ncdump /tmp/from_xr.nc 
netcdf from_xr {
dimensions:
    coor1 = 2 ;
    dim1 = 2 ;
variables:
    int64 coor1(coor1) ;
    double var1(coor1) ;
    double var2(dim1) ;
data:

 coor1 = 1, 2 ;

 var1 = 1, 2 ;

 var2 = 3, 4 ;
}
```

As `dim1` is not written in the file, xarray somehow knows?
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