open_mfdataset cannot open multiple netcdf files written by NASA/GEOS MAPL v1.0.0 that contain data on a cubed-sphere grid

MCVE Code Sample

First download these files:

• http://ftp.as.harvard.edu/gcgrid/geos-chem/1mo_benchmarks/GC_12/12.5.0/GCHP/diagnostics/GCHP.AerosolMass.20160716_1200z.nc4
• http://ftp.as.harvard.edu/gcgrid/geos-chem/1mo_benchmarks/GC_12/12.5.0/GCHP/diagnostics/GCHP.SpeciesConc.20160716_1200z.nc4

Then run this code:

import xarray as xr
filelist = ['GCHP.SpeciesConc.20160716_1200z.nc4', 'GCHP.AerosolMass.20160716_1200z.nc4']
ds = xr.open_mfdataset(filelist)
print(ds)

Expected Output

This should load data from both files into a single xarray Dataset object and print its contents.

Problem Description

Instead, this error occurs;

  File "./run_1mo_benchmark.py", line 479, in <module>
    ds = xr.open_mfdataset(filelist])
  File "/net/seasasfs02/srv/export/seasasfs02/share_root/ryantosca/python/geo/miniconda/envs/geo/lib/python3.6/site-packages/xarray/backends/api.py", line 719, in open_mfdataset
    ids=ids)
  File "/net/seasasfs02/srv/export/seasasfs02/share_root/ryantosca/python/geo/miniconda/envs/geo/lib/python3.6/site-packages/xarray/core/combine.py", line 553, in _auto_combine
    data_vars=data_vars, coords=coords)
  File "/net/seasasfs02/srv/export/seasasfs02/share_root/ryantosca/python/geo/miniconda/envs/geo/lib/python3.6/site-packages/xarray/core/combine.py", line 475, in _combine_nd
    compat=compat)
  File "/net/seasasfs02/srv/export/seasasfs02/share_root/ryantosca/python/geo/miniconda/envs/geo/lib/python3.6/site-packages/xarray/core/combine.py", line 493, in _auto_combine_all_along_first_dim
    data_vars, coords)
  File "/net/seasasfs02/srv/export/seasasfs02/share_root/ryantosca/python/geo/miniconda/envs/geo/lib/python3.6/site-packages/xarray/core/combine.py", line 514, in _auto_combine_1d
    merged = merge(concatenated, compat=compat)
  File "/net/seasasfs02/srv/export/seasasfs02/share_root/ryantosca/python/geo/miniconda/envs/geo/lib/python3.6/site-packages/xarray/core/merge.py", line 532, in merge
    variables, coord_names, dims = merge_core(dict_like_objects, compat, join)
  File "/net/seasasfs02/srv/export/seasasfs02/share_root/ryantosca/python/geo/miniconda/envs/geo/lib/python3.6/site-packages/xarray/core/merge.py", line 451, in merge_core
    variables = merge_variables(expanded, priority_vars, compat=compat)
  File "/net/seasasfs02/srv/export/seasasfs02/share_root/ryantosca/python/geo/miniconda/envs/geo/lib/python3.6/site-packages/xarray/core/merge.py", line 170, in merge_variables
    merged[name] = unique_variable(name, var_list, compat)
  File "/net/seasasfs02/srv/export/seasasfs02/share_root/ryantosca/python/geo/miniconda/envs/geo/lib/python3.6/site-packages/xarray/core/merge.py", line 90, in unique_variable
    % (name, out, var))
xarray.core.merge.MergeError: conflicting values for variable 'anchor' on objects to be combined:
first value: <xarray.Variable (nf: 6, ncontact: 4)>
dask.array<shape=(6, 4, 4), dtype=int32, chunksize=(6, 4, 4)>
Attributes:
    long_name:  anchor point
second value: <xarray.Variable (nf: 6, ncontact: 4)>
dask.array<shape=(6, 4, 4), dtype=int32, chunksize=(6, 4, 4)>
Attributes:
    long_name:  anchor point

It seems to get hung up on trying to merge the “anchor” variable. As a workaround, if I drop the “anchor” variable from both datasets and then use xr.open_mfdataset, then the merge works properly.

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.6.9 |Anaconda, Inc.| (default, Jul 30 2019, 19:07:31) [GCC 7.3.0] python-bits: 64 OS: Linux OS-release: 3.10.0-957.12.1.el7.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.2 libnetcdf: 4.6.1

xarray: 0.12.1 pandas: 0.25.1 numpy: 1.16.4 scipy: 1.3.1 netCDF4: 1.4.2 pydap: None h5netcdf: 0.6.2 h5py: 2.8.0 Nio: None zarr: None cftime: 1.0.3.4 nc_time_axis: None PseudonetCDF: None rasterio: None cfgrib: None iris: None bottleneck: 1.2.1 dask: 2.3.0 distributed: 2.3.2 matplotlib: 3.1.1 cartopy: 0.17.0 seaborn: 0.9.0 setuptools: 41.2.0 pip: 19.2.2 conda: None pytest: 4.2.0 IPython: 7.7.0 sphinx: 2.1.2

[dcherian]

@jhamman Hahaha.

[crusaderky]

Closing as a duplicate of #1378