issue_comments: 506288004

This data as json

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/pull/2706#issuecomment-506288004 https://api.github.com/repos/pydata/xarray/issues/2706 506288004 MDEyOklzc3VlQ29tbWVudDUwNjI4ODAwNA== 8643775 2019-06-27T10:21:53Z 2019-06-27T10:21:53Z NONE

adding a new variable currently errors if we don't provide the append_dim argument: ```python

import xarray as xr import pandas as pd ds0 = xr.Dataset({'temperature': (['time'], [50, 51, 52])}, coords={'time': pd.date_range('2000-01-01', periods=3)}) ds1 = xr.Dataset({'pressure': (['time'], [50, 51, 52])}, coords={'time': pd.date_range('2000-01-01', periods=3)}) store = dict() ds0.to_zarr(store, mode='w') <xarray.backends.zarr.ZarrStore object at 0x7fae926505c0> ds1.to_zarr(store, mode='a') Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/shikhar/code/xarray/xarray/core/dataset.py", line 1374, in to_zarr consolidated=consolidated, append_dim=append_dim) File "/home/shikhar/code/xarray/xarray/backends/api.py", line 1071, in to_zarr dump_to_store(dataset, zstore, writer, encoding=encoding) File "/home/shikhar/code/xarray/xarray/backends/api.py", line 928, in dump_to_store unlimited_dims=unlimited_dims) File "/home/shikhar/code/xarray/xarray/backends/zarr.py", line 366, in store unlimited_dims=unlimited_dims) File "/home/shikhar/code/xarray/xarray/backends/zarr.py", line 406, in set_variables "was not set".format(name) ValueError: variable 'time' already exists, but append_dim was not set ```

this works: ```python

import xarray as xr import pandas as pd ds0 = xr.Dataset({'temperature': (['time'], [50, 51, 52])}, coords={'time': pd.date_range('2000-01-01', periods=3)}) ds1 = xr.Dataset({'pressure': (['time'], [50, 51, 52])}, coords={'time': pd.date_range('2000-01-01', periods=3)}) store = dict() ds0.to_zarr(store, mode='w') <xarray.backends.zarr.ZarrStore object at 0x7fae926505c0> ds1.to_zarr(store, mode='a', append_dim='asdfasdf') xr.open_zarr(store) <xarray.Dataset> Dimensions: (time: 3) Coordinates: * time (time) datetime64[ns] 2000-01-01 2000-01-02 2000-01-03 Data variables: pressure (time) int64 dask.array<shape=(3,), chunksize=(3,)> temperature (time) int64 dask.array<shape=(3,), chunksize=(3,)> ```

will push a fix for this in a bit

 
{
    "total_count": 0,
    "+1": 0,
    "-1": 0,
    "laugh": 0,
    "hooray": 0,
    "confused": 0,
    "heart": 0,
    "rocket": 0,
    "eyes": 0
}
   402908148