What happened?

Calling xr.DataArray.diff with a non-existing dimension does not raise an exception.

What did you expect to happen?

An exception to be raised.

Minimal Complete Verifiable Example

Python import xarray as xr; import numpy as np; xr.DataArray(np.arange(10),dims=('a',)).diff('b')

MVCE confirmation

• [X] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• [X] Complete example — the example is self-contained, including all data and the text of any traceback.
• [X] Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• [X] New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

No response

Anything else we need to know?

No response

Environment

i.e. https://github.com/pydata/xarray/blob/5871637873cd83c3a656ee6f4df86ea6628cf68a/xarray/core/concat.py#L46

Arent' dims supposed to be any Hashable? In other xarray methods they generally are.

What happened?

I make a dataset with some variables, and make them all coordinates. Then I try to query on the dataset. Error ensues.

What did you expect to happen?

No error.

Minimal Complete Verifiable Example

```Python import xarray as xr import pandas as pd x = xr.Dataset.from_dataframe(pd.DataFrame(data=[[0,1],[2,3]],columns=['a','b']))

display(x.query(index='a==0')) #fine

y = x.set_coords(['a','b'])

display(y) #fine

y.query(index='a==0') #error ```

Relevant log output

```Python

KeyError Traceback (most recent call last) ~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/scope.py in resolve(self, key, is_local) 199 assert not is_local and not self.has_resolvers --> 200 return self.scope[key] 201 except KeyError:

~/miniconda3/lib/python3.9/collections/init.py in getitem(self, key) 940 pass --> 941 return self.missing(key) # support subclasses that define missing 942

~/miniconda3/lib/python3.9/collections/init.py in missing(self, key) 932 def missing(self, key): --> 933 raise KeyError(key) 934

KeyError: 'a'

During handling of the above exception, another exception occurred:

KeyError Traceback (most recent call last) ~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/scope.py in resolve(self, key, is_local) 205 # e.g., df[df > 0] --> 206 return self.temps[key] 207 except KeyError as err:

KeyError: 'a'

The above exception was the direct cause of the following exception:

UndefinedVariableError Traceback (most recent call last) /tmp/ipykernel_23733/4091370488.py in <cell line: 7>() 5 y = x.set_coords(['a','b']) 6 display(y) ----> 7 y.query(index='a==0')

~/miniconda3/lib/python3.9/site-packages/xarray/core/dataset.py in query(self, queries, parser, engine, missing_dims, **queries_kwargs) 7605 7606 # evaluate the queries to create the indexers -> 7607 indexers = { 7608 dim: pd.eval(expr, resolvers=[self], parser=parser, engine=engine) 7609 for dim, expr in queries.items()

~/miniconda3/lib/python3.9/site-packages/xarray/core/dataset.py in <dictcomp>(.0) 7606 # evaluate the queries to create the indexers 7607 indexers = { -> 7608 dim: pd.eval(expr, resolvers=[self], parser=parser, engine=engine) 7609 for dim, expr in queries.items() 7610 }

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/eval.py in eval(expr, parser, engine, truediv, local_dict, global_dict, resolvers, level, target, inplace) 348 ) 349 --> 350 parsed_expr = Expr(expr, engine=engine, parser=parser, env=env) 351 352 # construct the engine and evaluate the parsed expression

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in init(self, expr, engine, parser, env, level) 809 self.parser = parser 810 self._visitor = PARSERSparser --> 811 self.terms = self.parse() 812 813 @property

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in parse(self) 828 Parse an expression. 829 """ --> 830 return self._visitor.visit(self.expr) 831 832 @property

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit(self, node, kwargs) 413 method = "visit_" + type(node).name 414 visitor = getattr(self, method) --> 415 return visitor(node, kwargs) 416 417 def visit_Module(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit_Module(self, node, kwargs) 419 raise SyntaxError("only a single expression is allowed") 420 expr = node.body[0] --> 421 return self.visit(expr, kwargs) 422 423 def visit_Expr(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit(self, node, kwargs) 413 method = "visit_" + type(node).name 414 visitor = getattr(self, method) --> 415 return visitor(node, kwargs) 416 417 def visit_Module(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit_Expr(self, node, kwargs) 422 423 def visit_Expr(self, node, kwargs): --> 424 return self.visit(node.value, **kwargs) 425 426 def _rewrite_membership_op(self, node, left, right):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit(self, node, kwargs) 413 method = "visit_" + type(node).name 414 visitor = getattr(self, method) --> 415 return visitor(node, kwargs) 416 417 def visit_Module(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit_Compare(self, node, **kwargs) 721 op = self.translate_In(ops[0]) 722 binop = ast.BinOp(op=op, left=node.left, right=comps[0]) --> 723 return self.visit(binop) 724 725 # recursive case: we have a chained comparison, a CMP b CMP c, etc.

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit(self, node, kwargs) 413 method = "visit_" + type(node).name 414 visitor = getattr(self, method) --> 415 return visitor(node, kwargs) 416 417 def visit_Module(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit_BinOp(self, node, kwargs) 534 535 def visit_BinOp(self, node, kwargs): --> 536 op, op_class, left, right = self._maybe_transform_eq_ne(node) 537 left, right = self._maybe_downcast_constants(left, right) 538 return self._maybe_evaluate_binop(op, op_class, left, right)

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in _maybe_transform_eq_ne(self, node, left, right) 454 def _maybe_transform_eq_ne(self, node, left=None, right=None): 455 if left is None: --> 456 left = self.visit(node.left, side="left") 457 if right is None: 458 right = self.visit(node.right, side="right")

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit(self, node, kwargs) 413 method = "visit_" + type(node).name 414 visitor = getattr(self, method) --> 415 return visitor(node, kwargs) 416 417 def visit_Module(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit_Name(self, node, kwargs) 547 548 def visit_Name(self, node, kwargs): --> 549 return self.term_type(node.id, self.env, kwargs) 550 551 def visit_NameConstant(self, node, kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/ops.py in init(self, name, env, side, encoding) 96 tname = str(name) 97 self.is_local = tname.startswith(LOCAL_TAG) or tname in DEFAULT_GLOBALS ---> 98 self._value = self._resolve_name() 99 self.encoding = encoding 100

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/ops.py in _resolve_name(self) 113 114 def _resolve_name(self): --> 115 res = self.env.resolve(self.local_name, is_local=self.is_local) 116 self.update(res) 117

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/scope.py in resolve(self, key, is_local) 209 from pandas.core.computation.ops import UndefinedVariableError 210 --> 211 raise UndefinedVariableError(key, is_local) from err 212 213 def swapkey(self, old_key: str, new_key: str, new_value=None) -> None:

UndefinedVariableError: name 'a' is not defined ```

Anything else we need to know?

If the dataset has one data variable, then the error does not happen.

Environment

INSTALLED VERSIONS

commit: None python: 3.9.12 | packaged by conda-forge | (main, Mar 24 2022, 23:25:59) [GCC 10.3.0] python-bits: 64 OS: Linux OS-release: 4.19.0-19-amd64 machine: x86_64 processor: byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: ('en_US', 'UTF-8') libhdf5: 1.12.1 libnetcdf: 4.8.1

xarray: 2022.3.0 pandas: 1.4.1 numpy: 1.22.3 scipy: 1.8.0 netCDF4: 1.5.8 pydap: None h5netcdf: 1.0.0 h5py: 3.6.0 Nio: None zarr: 2.11.1 cftime: 1.5.2 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2022.03.0 distributed: 2022.3.0 matplotlib: 3.5.1 cartopy: None seaborn: 0.11.2 numbagg: None fsspec: 2022.02.0 cupy: None pint: 0.18 sparse: 0.13.0 setuptools: 59.8.0 pip: 22.0.4 conda: 4.12.0 pytest: 7.1.1 IPython: 7.32.0 sphinx: None

Trying to slice with sel using label delta values as interval, i.e. da.sel(mydim=slice(None,None,c).

What happened: The label delta value is not accepted.

What you expected to happen: Selecting c-spaced samples from the DataArray da.

Minimal Complete Verifiable Example:

```python dim0_n = 100 d = xr.DataArray(np.arange(dim0_n),coords={'dim0':np.linspace(0,1,num=dim0_n)},dims=('dim0',)) d.sel(dim0=slice(None,None,0.1))

expected 0,10,20,...,90

instead get a TypeError: 'float' object cannot be interpreted as an integer

(full traceback below)

```

Anything else we need to know?:

I think a warning in the documentation would be nice. It happened that I was giving integer values to c and xarray was subsetting datasets in an entirely different way that the one intended. It took noticing a downstream effect to find this behavior.

Environment:

https://github.com/pydata/xarray/blob/d4b7a608bab0e7c140937b0b59ca45115d205145/xarray/core/computation.py#L807

If a sequence, I get TypeError: Field elements must be 2- or 3-tuples, got 'dtype('float64')'

MVE ( WIP, will finish later )

```

p,v are chunked in 'time'

M is a positive integer

msd_w_one_mol takes two args, has two outputs

m,w = xr.apply_ufunc( msd_w_one_mol, p,v, input_core_dims=[('time','spatial'),('time',)], output_core_dims=[('interval',),('interval',)], vectorize=True, dask='parallelized', dask_gufunc_kwargs={ 'output_sizes':{'interval':M}, 'allow_rechunk':True,

'meta':(np.empty((M,),dtype=p.dtype),np.empty((M,),dtype=np.min_scalar_type(M)))

'output_dtypes':[p.dtype,np.min_scalar_type(M)],

},
output_dtypes=[p.dtype,np.min_scalar_type(M)] # error
output_dtypes=(p.dtype,np.min_scalar_type(M)) # works

)

```

Stack Trace: ```

ValueError Traceback (most recent call last) ~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/dask/array/gufunc.py in apply_gufunc(func, signature, args, kwargs) 429 try: --> 430 tmp = blockwise( # First try to compute meta 431 func, loop_output_dims, arginds, concatenate=True, **kwargs

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/dask/array/blockwise.py in blockwise(func, out_ind, name, token, dtype, adjust_chunks, new_axes, align_arrays, concatenate, meta, args, kwargs) 278 --> 279 meta = compute_meta(func, dtype, args[::2], **kwargs) 280 return new_da_object(graph, out, chunks, meta=meta, dtype=dtype)

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/dask/array/utils.py in compute_meta(func, _dtype, args, kwargs) 138 if isinstance(func, np.vectorize): --> 139 meta = func(args_meta) 140 else:

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/numpy/lib/function_base.py in call(self, args, *kwargs) 2112 -> 2113 return self._vectorize_call(func=func, args=vargs) 2114

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/numpy/lib/function_base.py in _vectorize_call(self, func, args) 2186 if self.signature is not None: -> 2187 res = self._vectorize_call_with_signature(func, args) 2188 elif not args:

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/numpy/lib/function_base.py in _vectorize_call_with_signature(self, func, args) 2260 for dim in dims): -> 2261 raise ValueError('cannot call vectorize with a signature ' 2262 'including new output dimensions on size 0 '

ValueError: cannot call vectorize with a signature including new output dimensions on size 0 inputs

During handling of the above exception, another exception occurred:

TypeError Traceback (most recent call last) <ipython-input-119-a2a3ac7df12d> in <module> ----> 1 m,w = xr.apply_ufunc( 2 msd_w_one_mol, 3 p,v, 4 input_core_dims=[('time','spatial'),('time',)], 5 output_core_dims=[('interval',),('interval',)],

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/xarray/core/computation.py in apply_ufunc(func, input_core_dims, output_core_dims, exclude_dims, vectorize, join, dataset_join, dataset_fill_value, keep_attrs, kwargs, dask, output_dtypes, output_sizes, meta, dask_gufunc_kwargs, args) 1126 # feed DataArray apply_variable_ufunc through apply_dataarray_vfunc 1127 elif any(isinstance(a, DataArray) for a in args): -> 1128 return apply_dataarray_vfunc( 1129 variables_vfunc, 1130 args,

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/xarray/core/computation.py in apply_dataarray_vfunc(func, signature, join, exclude_dims, keep_attrs, args) 269 270 data_vars = [getattr(a, "variable", a) for a in args] --> 271 result_var = func(data_vars) 272 273 if signature.num_outputs > 1:

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/xarray/core/computation.py in apply_variable_ufunc(func, signature, exclude_dims, dask, output_dtypes, vectorize, keep_attrs, dask_gufunc_kwargs, args) 722 ) 723 --> 724 result_data = func(input_data) 725 726 if signature.num_outputs == 1:

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/xarray/core/computation.py in func(*arrays) 690 import dask.array as da 691 --> 692 res = da.apply_gufunc( 693 numpy_func, 694 signature.to_gufunc_string(exclude_dims),

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/dask/array/gufunc.py in apply_gufunc(func, signature, args, *kwargs) 441 ) 442 else: --> 443 meta = tuple( 444 meta_from_array(sample, dtype=odt) 445 for ocd, odt in zip((output_coredimss,), (output_dtypes,))

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/dask/array/gufunc.py in <genexpr>(.0) 442 else: 443 meta = tuple( --> 444 meta_from_array(sample, dtype=odt) 445 for ocd, odt in zip((output_coredimss,), (output_dtypes,)) 446 )

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/dask/array/utils.py in meta_from_array(x, ndim, dtype) 104 meta = np.array(meta) 105 --> 106 if dtype and meta.dtype != dtype: 107 try: 108 meta = meta.astype(dtype)

TypeError: Field elements must be 2- or 3-tuples, got 'dtype('float64')' ```

Preliminary investigation using %debug: ```

~/dotfiles/conda/base/.conda/lib/python3.8/site-packages/dask/array/utils.py(106)meta_from_array() 104 meta = np.array(meta) 105 --> 106 if dtype and meta.dtype != dtype: 107 try: 108 meta = meta.astype(dtype)

ipdb> print(dtype)

[dtype('float64'), dtype('uint16')]

ipdb> print(meta.dtype)

float64

ipdb> print(dtype)

[dtype('float64'), dtype('uint16')]

```