issues

We can't open the IOOS New England triangular mesh ocean forecasts with Xarray because it doesn't understand their more complex CF vertical coordinate system.

python import xarray as xr url='http://www.smast.umassd.edu:8080/thredds/dodsC/FVCOM/NECOFS/Forecasts/NECOFS_GOM3_FORECAST.nc' xr.open_dataset(url) fails with: MissingDimensionsError: 'siglay' has more than 1-dimension and the same name as one of its dimensions ('siglay', 'node'). xarray disallows such variables because they conflict with the coordinates used to label dimensions. If you open this dataset with nc = netCDF4.Dataset(url) you can see what the data variables (e.g. temp) and coordinates (e.g. siglay) look like: ``` print(nc['temp'])

<class 'netCDF4._netCDF4.Variable'> float32 temp(time, siglay, node) long_name: temperature standard_name: sea_water_potential_temperature units: degrees_C coordinates: time siglay lat lon type: data coverage_content_type: modelResult mesh: fvcom_mesh location: node unlimited dimensions: time current shape = (145, 40, 53087)

print(nc['siglay'])

<class 'netCDF4._netCDF4.Variable'> float32 siglay(siglay, node) long_name: Sigma Layers standard_name: ocean_sigma_coordinate positive: up valid_min: -1.0 valid_max: 0.0 formula_terms: sigma: siglay eta: zeta depth: h unlimited dimensions: current shape = (40, 53087) `` So thesiglayvariable in this dataset specifies the fraction of water column contained in the layer and because this fraction changes over the grid, it has dimensions ofsiglayandnode. The variablesiglayis just one of the variables used in the calculation of this CF-compliant vertical coordinate. The actual vertical coordinate (after computation viaformula_terms`) ends up being 4D.

While we understand that there is no way to represent the vertical coordinate with a one-dimensional coordinate that xarray would like, it would be nice if there way to at least load the variable array data like temp into xarray. We tried: ds = xr.open_dataset(url,decode_times=False, decode_coords=False, decode_cf=False) and we get the same error.

Is there any workaround for this?

It's considered best practice to create cloud-optimized geotiff (COG) with overviews, which are essentially copies of the dataset at different resolutions to allow fast representation at different scales.

It would be nice if we could pick a specific overview using xr.read_rasterio, perhaps by just an additional parameter on the call, like xr.read_rasterio(url, overview=512) or something.

Currently we need to use Rasterio to find out what the overlays are, for example: python url = 'https://esip-pangeo-uswest2.s3-us-west-2.amazonaws.com/sciencebase/Southern_California_Topobathy_DEM_1m_cog.tif' src = rasterio.open(url, 'r') [src.overviews(i) for i in src.indexes] which results in: [[4, 8, 16, 32, 64, 128, 256, 512, 1023]] See the notebook here for the hack workaround to extract an overlay from COG: https://nbviewer.jupyter.org/gist/rsignell-usgs/dc4cf94fae97d085f6f2b9b896ec5336

I've been making good use of the zarr backend via xr.open_zarr, but with the National Water Model datasets I've been working with lately, it would be really handy to be able to open them with xr.open_mfdataset(filelist, engine='znetcdf') so that we could more easily create xarray datasets from the assemblage of overlapping forecast data files.

So just as we have h5netcdf "Pythonic interface to netCDF4 via h5py", we could have "z5netcdf", a "Pythonic interface to netCDF4 via Zarr".

I see that @shoyer previously had this idea: https://github.com/pydata/xarray/issues/1223#issuecomment-274230041 and also @rabernat https://github.com/pydata/xarray/pull/1528#issuecomment-325226495 thinks it would be a good idea, so I'm just piling on from a user perspective!

This simple xarray ufunc to calculate wind speed worked under xarray=0.12.3: python import xarray as xr url = 'http://thredds.ucar.edu/thredds/dodsC/grib/NCEP/HRRR/CONUS_2p5km/Best' ds = xr.open_dataset(url, chunks={'time1':1}) windspeed = xr.ufuncs.sqrt(ds['u-component_of_wind_height_above_ground']**2 + ds['v-component_of_wind_height_above_ground']**2) but with xarray=0.13.0, merge_variables fails and dumps this traceback:

```python-traceback

ValueError Traceback (most recent call last) <ipython-input-4-2ac66965ccfc> in <module> ----> 1 windspeed = xr.ufuncs.sqrt(ds['u-component_of_wind_height_above_ground']2 + ds['v-component_of_wind_height_above_ground']2)

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/core/dataarray.py in func(self, other) 2495 else f(other_variable, self.variable) 2496 ) -> 2497 coords = self.coords._merge_raw(other_coords) 2498 name = self._result_name(other) 2499

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/core/coordinates.py in _merge_raw(self, other) 128 else: 129 # don't align because we already called xarray.align --> 130 variables = expand_and_merge_variables([self.variables, other.variables]) 131 return variables 132

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/core/merge.py in expand_and_merge_variables(objs, priority_arg) 380 expanded = expand_variable_dicts(objs) 381 priority_vars = _get_priority_vars(objs, priority_arg) --> 382 variables = merge_variables(expanded, priority_vars) 383 return variables 384

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/core/merge.py in merge_variables(list_of_variables_dicts, priority_vars, compat) 202 else: 203 try: --> 204 merged[name] = unique_variable(name, var_list, compat) 205 except MergeError: 206 if compat != "minimal":

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/core/merge.py in unique_variable(name, variables, compat, equals) 116 out = out.compute() 117 for var in variables[1:]: --> 118 equals = getattr(out, compat)(var) 119 if not equals: 120 break

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/core/variable.py in broadcast_equals(self, other, equiv) 1574 except (ValueError, AttributeError): 1575 return False -> 1576 return self.equals(other, equiv=equiv) 1577 1578 def identical(self, other):

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/core/variable.py in equals(self, other, equiv) 1558 try: 1559 return self.dims == other.dims and ( -> 1560 self._data is other._data or equiv(self.data, other.data) 1561 ) 1562 except (TypeError, AttributeError):

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/core/duck_array_ops.py in array_equiv(arr1, arr2) 200 with warnings.catch_warnings(): 201 warnings.filterwarnings("ignore", "In the future, 'NAT == x'") --> 202 flag_array = (arr1 == arr2) | (isnull(arr1) & isnull(arr2)) 203 return bool(flag_array.all()) 204

/srv/conda/envs/notebook/lib/python3.7/site-packages/dask/array/core.py in eq(self, other) 1740 1741 def eq(self, other): -> 1742 return elemwise(operator.eq, self, other) 1743 1744 def gt(self, other):

/srv/conda/envs/notebook/lib/python3.7/site-packages/dask/array/core.py in elemwise(op, args, kwargs) 3765 for a in args 3766 ), -> 3767 *blockwise_kwargs 3768 ) 3769

/srv/conda/envs/notebook/lib/python3.7/site-packages/dask/array/blockwise.py in blockwise(func, out_ind, name, token, dtype, adjust_chunks, new_axes, align_arrays, concatenate, meta, args, kwargs) 143 144 if align_arrays: --> 145 chunkss, arrays = unify_chunks(args) 146 else: 147 arginds = [(a, i) for (a, i) in toolz.partition(2, args) if i is not None]

/srv/conda/envs/notebook/lib/python3.7/site-packages/dask/array/core.py in unify_chunks(args, *kwargs) 3034 3035 arginds = [ -> 3036 (asanyarray(a) if ind is not None else a, ind) for a, ind in partition(2, args) 3037 ] # [x, ij, y, jk] 3038 args = list(concat(arginds)) # [(x, ij), (y, jk)]

/srv/conda/envs/notebook/lib/python3.7/site-packages/dask/array/core.py in <listcomp>(.0) 3034 3035 arginds = [ -> 3036 (asanyarray(a) if ind is not None else a, ind) for a, ind in partition(2, args) 3037 ] # [x, ij, y, jk] 3038 args = list(concat(arginds)) # [(x, ij), (y, jk)]

/srv/conda/envs/notebook/lib/python3.7/site-packages/dask/array/core.py in asanyarray(a) 3609 elif hasattr(a, "to_dask_array"): 3610 return a.to_dask_array() -> 3611 elif hasattr(a, "data") and type(a).module.startswith("xarray."): 3612 return asanyarray(a.data) 3613 elif isinstance(a, (list, tuple)) and any(isinstance(i, Array) for i in a):

ValueError: cannot include dtype 'M' in a buffer ```

Is this a bug or a feature that I should be handling differently in my code?

Output of xr.show_versions()

@jhamman suggested I raise this SO question as an issue here.

I have a dataset that looks like: <xarray.Dataset> Dimensions: (nv: 2, reference_time: 746, time: 746, x: 4608, y: 3840) Coordinates: * reference_time (reference_time) datetime64[ns] 2018-03-07 ... * x (x) float64 -2.304e+06 -2.303e+06 -2.302e+06 ... * y (y) float64 -1.92e+06 -1.919e+06 -1.918e+06 ... * time (time) datetime64[ns] 2018-03-07T01:00:00 ... Dimensions without coordinates: nv Data variables: time_bounds (time, nv) datetime64[ns] dask.array<shape=(746, 2), chunksize=(1, 2)> ProjectionCoordinateSystem (time) |S64 b'' b'' b'' b'' b'' b'' b'' b'' ... T2D (time, y, x) float64 dask.array<shape=(746, 3840, 4608), chunksize=(1, 3840, 4608)>

When writing this dataset using ds.to_zarr containing the ProjectionCoordinateSystem variable with dtype=S64 , there can be an issue reading it using ds.open_zarr with the default auto_chunk=True.

This example illustrates the problem: ```python import xarray as xr import s3fs

f_zarr = 'rsignell/nwm/test02'
fs = s3fs.S3FileSystem(anon=False) d = s3fs.S3Map(f_zarr, s3=fs) xr.open_zarr(d) returningpython-traceback

ValueError Traceback (most recent call last) <ipython-input-3-fff1cd753e7c> in <module>() 2 fs = s3fs.S3FileSystem(anon=False) 3 d = s3fs.S3Map(f_zarr, s3=fs) ----> 4 xr.open_zarr(d)

/opt/conda/lib/python3.6/site-packages/xarray/backends/zarr.py in open_zarr(store, group, synchronizer, auto_chunk, decode_cf, mask_and_scale, decode_times, concat_characters, decode_coords, drop_variables) 476 477 variables = OrderedDict([(k, maybe_chunk(k, v)) --> 478 for k, v in ds.variables.items()]) 479 return ds._replace_vars_and_dims(variables) 480 else:

/opt/conda/lib/python3.6/site-packages/xarray/backends/zarr.py in <listcomp>(.0) 476 477 variables = OrderedDict([(k, maybe_chunk(k, v)) --> 478 for k, v in ds.variables.items()]) 479 return ds._replace_vars_and_dims(variables) 480 else:

/opt/conda/lib/python3.6/site-packages/xarray/backends/zarr.py in maybe_chunk(name, var) 471 token2 = tokenize(name, var._data) 472 name2 = 'zarr-%s' % token2 --> 473 return var.chunk(chunks, name=name2, lock=None) 474 else: 475 return var

/opt/conda/lib/python3.6/site-packages/xarray/core/variable.py in chunk(self, chunks, name, lock) 820 data = indexing.ImplicitToExplicitIndexingAdapter( 821 data, indexing.OuterIndexer) --> 822 data = da.from_array(data, chunks, name=name, lock=lock) 823 824 return type(self)(self.dims, data, self._attrs, self._encoding,

/opt/conda/lib/python3.6/site-packages/dask/array/core.py in from_array(x, chunks, name, lock, asarray, fancy, getitem) 1988 >>> a = da.from_array(x, chunks=(1000, 1000), lock=True) # doctest: +SKIP 1989 """ -> 1990 chunks = normalize_chunks(chunks, x.shape) 1991 if name in (None, True): 1992 token = tokenize(x, chunks)

/opt/conda/lib/python3.6/site-packages/dask/array/core.py in normalize_chunks(chunks, shape) 1918 raise ValueError( 1919 "Chunks and shape must be of the same length/dimension. " -> 1920 "Got chunks=%s, shape=%s" % (chunks, shape)) 1921 1922 if shape is not None:

ValueError: Chunks and shape must be of the same length/dimension. Got chunks=(3, 64), shape=(3,) ``` The full notebook is at https://gist.github.com/rsignell-usgs/dce09aae4f7cd174a141247a56ddea2c

Is there a way to return the data variables that match a specified standard_name?

I came up with this, but maybe the functionality already exists or there is a better way.

def get_std_name_vars(ds,std_name): return {k: v for k, v in ds.data_vars.iteritems() if 'standard_name' in v.attrs.keys() and std_name in v.standard_name}

as in this example: http://nbviewer.ipython.org/gist/rsignell-usgs/5b263906e92ce47bf05e

In this notebook: http://nbviewer.ipython.org/gist/rsignell-usgs/047235496029529585cc, the ds.to_netcdf method in cell [12] is failing for this dataset with a single time value:

``` /home/usgs/miniconda/envs/ioos/lib/python2.7/site-packages/xray/conventions.pyc in infer_datetime_units(dates) 185 unique_timedeltas = np.unique(np.diff(dates[pd.notnull(dates)])) 186 units = _infer_time_units_from_diff(unique_timedeltas) --> 187 return '%s since %s' % (units, pd.Timestamp(dates[0])) 188 189

IndexError: too many indices for array ```

When there is a single value, I guess dates must not be an array.