MergeError: coordinate mytime1 shares a name with a dataset dimension …. This is disallowed by the xarray data model.

[ahmedshaaban1]

import xarray as xr
import pandas as p
import numpy as np

var1 = np.ones((364))
tt1=p.date_range('1/1/2018','12/30/2018')
tt1.name= 'time1_name'

var=xr.Dataset(
		data_vars={
			'var1':(('mytime1'),var1),
			},
		coords={
			'mytime1':tt1,
			}
)

Problem description

I got the following error "MergeError: coordinate mytime1 shares a name with a dataset dimension, but is not a 1D variable along that dimension. This is disallowed by the xarray data model." when I inlcude name attribue "time1_name" to the var1 dimension mytime1.

Expected Output

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 2.7.14.final.0 python-bits: 64 OS: Darwin OS-release: 18.5.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: en_US.UTF-8 LANG: en_US.UTF-8 LOCALE: en_US.UTF-8

xarray: 0.10.9
pandas: 0.23.4
numpy: 1.14.2
scipy: 1.0.0
netCDF4: 1.3.1
h5netcdf: None
h5py: 2.7.1
Nio: None
zarr: None
cftime: None
PseudonetCDF: None
rasterio: None
iris: None
bottleneck: 1.2.1
cyordereddict: None
dask: 0.16.1
distributed: 1.20.2
matplotlib: 2.1.2
cartopy: 0.16.0
seaborn: 0.8.1
setuptools: 40.8.0
pip: 18.1
conda: 4.4.10
pytest: 3.3.2
IPython: 5.4.1
sphinx: 1.6.6

[TomNicholas]

So in xarray coordinates which have the same name as dimensions are given special status - they are known as "dimension coordinates". (Yes this is confusing and I think there are plans to make this structure clearer in the future.)

Dimension coordinates have to be 1D along the corresponding dimension, as indicated by the error message. However in your example you didn't specify the dimension which you want the coordinate tt1 to have, because you didn't put it in a tuple with the desired dimensions like you did with the variable var1. If you add the desired dimension in then the error is no longer thrown, and I think gives you the dataset you want:

import xarray as xr
import pandas as p
import numpy as np

var1 = np.ones((364))
tt1=p.date_range('1/1/2018','12/30/2018')
tt1.name= 'time1_name'

var=xr.Dataset(
		data_vars={
			'var1':(('mytime1'),var1),
			},
		coords={
			'mytime1':(('mytime1'), tt1),
			}
)

which when printed gives

<xarray.Dataset>
Dimensions:  (mytime1: 364)
Coordinates:
  * mytime1  (mytime1) datetime64[ns] 2018-01-01 2018-01-02 ... 2018-12-30
Data variables:
    var1     (mytime1) float64 1.0 1.0 1.0 1.0 1.0 1.0 ... 1.0 1.0 1.0 1.0 1.0

[ahmedshaaban1]

Thanks ... in case I used delattr to delete the name so that I can avoid the error message, then what is the difference between specifing or ignoring the dimnsion that the coordinate is attached.
coords={ 'mytime1':(('mytime1'), tt1), }
and
coords={ 'mytime1': tt1, }

[shoyer]

Yes, we'd like to remove this "feature" -- see #2368 for more discussion