Get a virtual variable (e.g., 'time.year') from a dict of xarray.Variable objects (if possible)
(
variables, key: Hashable, dim_sizes: Mapping | None = None
)
| 55 | |
| 56 | |
| 57 | def _get_virtual_variable( |
| 58 | variables, key: Hashable, dim_sizes: Mapping | None = None |
| 59 | ) -> tuple[Hashable, Hashable, Variable]: |
| 60 | """Get a virtual variable (e.g., 'time.year') from a dict of xarray.Variable |
| 61 | objects (if possible) |
| 62 | |
| 63 | """ |
| 64 | from xarray.core.dataarray import DataArray |
| 65 | |
| 66 | if dim_sizes is None: |
| 67 | dim_sizes = {} |
| 68 | |
| 69 | if key in dim_sizes: |
| 70 | data = pd.RangeIndex(dim_sizes[key], name=key) |
| 71 | variable = IndexVariable((key,), data, fastpath=True) |
| 72 | return key, key, variable |
| 73 | |
| 74 | if not isinstance(key, str): |
| 75 | raise KeyError(key) |
| 76 | |
| 77 | split_key = key.split(".", 1) |
| 78 | if len(split_key) != 2: |
| 79 | raise KeyError(key) |
| 80 | |
| 81 | ref_name, var_name = split_key |
| 82 | ref_var = variables[ref_name] |
| 83 | |
| 84 | if _contains_datetime_like_objects(ref_var): |
| 85 | ref_var = DataArray(ref_var) |
| 86 | data = getattr(ref_var.dt, var_name).data |
| 87 | else: |
| 88 | data = getattr(ref_var, var_name).data |
| 89 | virtual_var = Variable(ref_var.dims, data) |
| 90 | |
| 91 | return ref_name, var_name, virtual_var |
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