issues

What happened: I am trying to write into a zarr a dataset by reading each timesteps and write this time step into a zarr store. For that I prepared the dataset and filled the variable values with 0s and wrote the store with mode='a'. I then perform the operations I need on each variables and try to write the time step of the dataset.

ds.isel(time=t).to_zarr(outfile, region={"time": t})

However I received this error message: ValueError: all keys in ``region`` are not in Dataset dimensions, got ['time'] and ['cell', 'face', 'layer', 'max_cell_node', 'max_face_nodes', 'node', 'siglay'] But

```python

In: ds.dims Out: Frozen(SortedKeysDict({'time': 1465, 'node': 112015, 'layer': 6, 'face': 198364, 'max_face_nodes': 3, 'cell': 991820, 'max_cell_node': 6, 'siglay': 6}))

```

Checking in the API, it comes from ```python

~/.local/lib/python3.8/site-packages/xarray/backends/api.py in _validate_append_dim_and_encoding(ds_to_append, store, append_dim, region, encoding, **open_kwargs) 1330 for k, v in region.items(): 1331 if k not in ds_to_append.dims: -> 1332 raise ValueError( 1333 f"all keys in region are not in Dataset dimensions, got " 1334 f"{list(region)} and {list(ds_to_append.dims)}" ```

What you expected to happen: Incremently append data to the zarr store

Minimal Complete Verifiable Example:

```python import xarray as xr from datetime import datetime,timedelta import numpy as np dt= datetime.now() times= np.arange(dt,dt+timedelta(days=6), timedelta(hours=1)) nodesx,nodesy,layers=np.arange(10,50), np.arange(10,50)+15, np.arange(10) ds=xr.Dataset() ds.coords['time']=('time', times) ds.coords['node_x']=('node', nodesx) ds.coords['node_y']=('node', nodesy) ds.coords['layer']=('layer', layers) outfile='my_zarr' varnames=['potato','banana', 'apple'] for var in varnames: ds[var]=(('time', 'layer', 'node'), np.zeros((len(times), len(layers),len(nodesx)))) ds.to_zarr(outfile, mode='a') for t in range(len(times)): for var in varnames: ds[var].isel(time=t).values += np.random.random((len(layers),len(nodesx))) ds.isel(time=t).to_zarr(outfile, region={"time": t})

ValueError Traceback (most recent call last) <ipython-input-25-8baf03aa01a3> in <module> 2 for var in varnames: 3 ds[var].isel(time=t).values += np.random.random((len(layers),len(nodesx))) ----> 4 ds.isel(time=t).to_zarr(outfile, region={"time": t}) 5

~/.local/lib/python3.8/site-packages/xarray/core/dataset.py in to_zarr(self, store, chunk_store, mode, synchronizer, group, encoding, compute, consolidated, append_dim, region) 1743 encoding = {} 1744 -> 1745 return to_zarr( 1746 self, 1747 store=store,

~/.local/lib/python3.8/site-packages/xarray/backends/api.py in to_zarr(dataset, store, chunk_store, mode, synchronizer, group, encoding, compute, consolidated, append_dim, region) 1457 if mode == "a": 1458 _validate_datatypes_for_zarr_append(dataset) -> 1459 _validate_append_dim_and_encoding( 1460 dataset, 1461 store,

~/.local/lib/python3.8/site-packages/xarray/backends/api.py in _validate_append_dim_and_encoding(ds_to_append, store, append_dim, region, encoding, **open_kwargs) 1330 for k, v in region.items(): 1331 if k not in ds_to_append.dims: -> 1332 raise ValueError( 1333 f"all keys in region are not in Dataset dimensions, got " 1334 f"{list(region)} and {list(ds_to_append.dims)}"

ValueError: all keys in region are not in Dataset dimensions, got ['time'] and ['layer', 'node'] ```

Anything else we need to know?:

Environment: