Fix DataArrayRolling.__iter__ with center=True

doc/whats-new.rst

@@ -54,6 +54,9 @@ Bug fixes
 - :py:meth:`open_dataset` with dask and ``~`` in the path now resolves the home directory
   instead of raising an error. (:issue:`6707`, :pull:`6710`)
   By `Michael Niklas <https://github.com/headtr1ck>`_.
+- :py:meth:`DataArrayRolling.__iter__` with ``center=True`` now works correctly.
+  (:issue:`6739`, :pull:`6744`)
+  By `Michael Niklas <https://github.com/headtr1ck>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/core/rolling.py

@@ -267,12 +267,15 @@ def __init__(
         # TODO legacy attribute
         self.window_labels = self.obj[self.dim[0]]
 
-    def __iter__(self) -> Iterator[tuple[RollingKey, DataArray]]:
+    def __iter__(self) -> Iterator[tuple[DataArray, DataArray]]:
         if self.ndim > 1:
             raise ValueError("__iter__ is only supported for 1d-rolling")
-        stops = np.arange(1, len(self.window_labels) + 1)
+
+        offset = int(self.window[0] + 1) // 2 if self.center[0] else 1
+        stops = np.arange(offset, self.obj.sizes[self.dim[0]] + offset)
         starts = stops - int(self.window[0])
-        starts[: int(self.window[0])] = 0
+        starts[: int(self.window[0]) - offset] = 0
+
         for (label, start, stop) in zip(self.window_labels, starts, stops):
             window = self.obj.isel({self.dim[0]: slice(start, stop)})