Add RangeIndex (#10076)

Co-authored-by: Deepak Cherian <dcherian@users.noreply.github.com>

Author: benbovy

doc/api-hidden.rst

@@ -530,6 +530,10 @@
    Index.rename
    Index.copy
 
+   indexes.RangeIndex.start
+   indexes.RangeIndex.stop
+   indexes.RangeIndex.step
+
    backends.NetCDF4DataStore.close
    backends.NetCDF4DataStore.encode
    backends.NetCDF4DataStore.encode_attribute

doc/api.rst

@@ -1573,6 +1573,7 @@ Custom Indexes
    :toctree: generated/
 
    CFTimeIndex
+   indexes.RangeIndex
 
 Creating custom indexes
 -----------------------
@@ -1582,6 +1583,8 @@ Creating custom indexes
    cftime_range
    date_range
    date_range_like
+   indexes.RangeIndex.arange
+   indexes.RangeIndex.linspace
 
 Tutorial
 ========

doc/whats-new.rst

@@ -62,9 +62,11 @@ Andrecho, Deepak Cherian, Ian Hunt-Isaak, Karl Krauth, Mathias Hauser, Maximilia
 
 New Features
 ~~~~~~~~~~~~
-
 - Allow setting a ``fill_value`` for Zarr format 3 arrays. Specify ``fill_value`` in ``encoding`` as usual.
   (:issue:`10064`). By `Deepak Cherian <https://github.com/dcherian>`_.
+- Added :py:class:`indexes.RangeIndex` as an alternative, memory saving Xarray index representing
+  a 1-dimensional bounded interval with evenly spaced floating values (:issue:`8473`, :pull:`10076`).
+  By `Benoit Bovy <https://github.com/benbovy>`_.
 
 Breaking changes
 ~~~~~~~~~~~~~~~~

xarray/core/formatting.py

@@ -312,7 +312,7 @@ def inline_variable_array_repr(var, max_width):
 def summarize_variable(
     name: Hashable,
     var: Variable,
-    col_width: int,
+    col_width: int | None = None,
     max_width: int | None = None,
     is_index: bool = False,
 ):
@@ -327,7 +327,9 @@ def summarize_variable(
             max_width = max_width_options
 
     marker = "*" if is_index else " "
-    first_col = pretty_print(f"  {marker} {name} ", col_width)
+    first_col = f"  {marker} {name} "
+    if col_width is not None:
+        first_col = pretty_print(first_col, col_width)
 
     if variable.dims:
         dims_str = "({}) ".format(", ".join(map(str, variable.dims)))

xarray/core/indexes.py

@@ -1500,8 +1500,21 @@ def rename(
         name_dict: Mapping[Any, Hashable],
         dims_dict: Mapping[Any, Hashable],
     ) -> Self:
-        # TODO: maybe update self.transform coord_names, dim_size and dims attributes
-        return self
+        coord_names = self.transform.coord_names
+        dims = self.transform.dims
+        dim_size = self.transform.dim_size
+
+        if not set(coord_names) & set(name_dict) and not set(dims) & set(dims_dict):
+            return self
+
+        new_transform = copy.deepcopy(self.transform)
+        new_transform.coord_names = tuple(name_dict.get(n, n) for n in coord_names)
+        new_transform.dims = tuple(str(dims_dict.get(d, d)) for d in dims)
+        new_transform.dim_size = {
+            str(dims_dict.get(d, d)): v for d, v in dim_size.items()
+        }
+
+        return type(self)(new_transform)
 
 
 def create_default_index_implicit(

xarray/core/indexing.py

@@ -240,16 +240,16 @@ def expanded_indexer(key, ndim):
     return tuple(new_key)
 
 
-def _normalize_slice(sl: slice, size: int) -> slice:
+def normalize_slice(sl: slice, size: int) -> slice:
     """
     Ensure that given slice only contains positive start and stop values
     (stop can be -1 for full-size slices with negative steps, e.g. [-10::-1])
 
     Examples
     --------
-    >>> _normalize_slice(slice(0, 9), 10)
+    >>> normalize_slice(slice(0, 9), 10)
     slice(0, 9, 1)
-    >>> _normalize_slice(slice(0, -1), 10)
+    >>> normalize_slice(slice(0, -1), 10)
     slice(0, 9, 1)
     """
     return slice(*sl.indices(size))
@@ -266,7 +266,7 @@ def _expand_slice(slice_: slice, size: int) -> np.ndarray[Any, np.dtype[np.integ
     >>> _expand_slice(slice(0, -1), 10)
     array([0, 1, 2, 3, 4, 5, 6, 7, 8])
     """
-    sl = _normalize_slice(slice_, size)
+    sl = normalize_slice(slice_, size)
     return np.arange(sl.start, sl.stop, sl.step)
 
 
@@ -275,14 +275,14 @@ def slice_slice(old_slice: slice, applied_slice: slice, size: int) -> slice:
     index it with another slice to return a new slice equivalent to applying
     the slices sequentially
     """
-    old_slice = _normalize_slice(old_slice, size)
+    old_slice = normalize_slice(old_slice, size)
 
     size_after_old_slice = len(range(old_slice.start, old_slice.stop, old_slice.step))
     if size_after_old_slice == 0:
         # nothing left after applying first slice
         return slice(0)
 
-    applied_slice = _normalize_slice(applied_slice, size_after_old_slice)
+    applied_slice = normalize_slice(applied_slice, size_after_old_slice)
 
     start = old_slice.start + applied_slice.start * old_slice.step
     if start < 0:

xarray/indexes/__init__.py

@@ -8,5 +8,6 @@
     PandasIndex,
     PandasMultiIndex,
 )
+from xarray.indexes.range_index import RangeIndex
 
-__all__ = ["Index", "PandasIndex", "PandasMultiIndex"]
+__all__ = ["Index", "PandasIndex", "PandasMultiIndex", "RangeIndex"]