Class CoordinateTransformIndex

xarray/core/indexes.py:1486–1627

Helper class for creating Xarray indexes based on coordinate transforms. - wraps a :py:class:`CoordinateTransform` instance - takes care of creating the index (lazy) coordinates - supports point-wise label-based selection - supports exact alignment only, by comparing indexes based o

class CoordinateTransformIndex(Index):
    """Helper class for creating Xarray indexes based on coordinate transforms.

    - wraps a :py:class:`CoordinateTransform` instance
    - takes care of creating the index (lazy) coordinates
    - supports point-wise label-based selection
    - supports exact alignment only, by comparing indexes based on their transform
      (not on their explicit coordinate labels)

    .. caution::
        This API is experimental and subject to change. Please report any bugs or surprising
        behaviour you encounter.
    """

    transform: CoordinateTransform

    def __init__(
        self,
        transform: CoordinateTransform,
    ):
        self.transform = transform

    def create_variables(
        self, variables: Mapping[Any, Variable] | None = None
    ) -> IndexVars:
        from xarray.core.variable import Variable

        new_variables = {}

        for name in self.transform.coord_names:
            # copy attributes, if any
            attrs: Mapping[Hashable, Any] | None

            if variables is not None and name in variables:
                var = variables[name]
                attrs = var.attrs
            else:
                attrs = None

            data = CoordinateTransformIndexingAdapter(self.transform, name)
            new_variables[name] = Variable(self.transform.dims, data, attrs=attrs)

        return new_variables

    def isel(
        self, indexers: Mapping[Any, int | slice | np.ndarray | Variable]
    ) -> Index | None:
        # TODO: support returning a new index (e.g., possible to re-calculate the
        # the transform or calculate another transform on a reduced dimension space)
        return None

    def sel(
        self, labels: dict[Any, Any], method=None, tolerance=None
    ) -> IndexSelResult:
        from xarray.core.dataarray import DataArray
        from xarray.core.variable import Variable

        if method != "nearest":