fix: preserve RangeIndex.arange step

doc/whats-new.rst

@@ -29,6 +29,8 @@ Bug Fixes
 - Fix a major performance regression in :py:meth:`Coordinates.to_index` (and
   consequently :py:meth:`Dataset.to_dataframe`) caused by converting the cached
   code ndarrays into Python lists (:issue:`11305`).
+- Preserve the requested spacing when :py:meth:`xarray.indexes.RangeIndex.arange`
+  is called with a step that does not evenly divide the interval (:issue:`11325`).
 
 
 Documentation

xarray/indexes/range_index.py

@@ -132,9 +132,9 @@ def slice(self, sl: slice) -> "RangeCoordinateTransform":
             self.dim,
             dtype=self.dtype,
         )
-        if new_size == 0:
-            # For empty slices, preserve step from parent
-            result._step = self.step
+        # Preserve the logical slice spacing without carrying small binary
+        # multiplication artifacts into materialized coordinates.
+        result._step = round(self.step * new_range.step, 15)
         return result
 
 
@@ -281,6 +281,7 @@ def arange(
         transform = RangeCoordinateTransform(
             start, stop, size, coord_name, dim, dtype=dtype
         )
+        transform._step = step
 
         return cls(transform)
 

xarray/tests/test_range_index.py

@@ -30,6 +30,7 @@ def create_dataset_arange(
         ((), {"start": 2.0, "stop": 10.0}),
         ((2.0, 10.0, 2.0), {}),
         ((), {"start": 2.0, "stop": 10.0, "step": 2.0}),
+        ((0.0, 1.0, 0.3), {}),
     ],
 )
 def test_range_index_arange(args, kwargs) -> None: