pydata · eshort0401 · Nov 21, 2025 · Nov 21, 2025 · Nov 21, 2025 · Nov 21, 2025
diff --git a/doc/api/dataarray.rst b/doc/api/dataarray.rst
@@ -162,6 +162,7 @@ Aggregation
    DataArray.min
    DataArray.mean
    DataArray.median
+   DataArray.nunique
    DataArray.prod
    DataArray.sum
    DataArray.std

diff --git a/doc/api/dataset.rst b/doc/api/dataset.rst
@@ -169,6 +169,7 @@ Aggregation
    Dataset.min
    Dataset.mean
    Dataset.median
+   Dataset.nunique
    Dataset.prod
    Dataset.sum
    Dataset.std

diff --git a/doc/api/datatree.rst b/doc/api/datatree.rst
@@ -266,6 +266,7 @@ Aggregate data in all nodes in the subtree simultaneously.
    DataTree.min
    DataTree.mean
    DataTree.median
+   DataTree.nunique
    DataTree.prod
    DataTree.sum
    DataTree.std

diff --git a/doc/whats-new.rst b/doc/whats-new.rst
@@ -17,6 +17,10 @@ New Features
 - :py:func:`combine_nested` now support :py:class:`DataTree` objects
   (:pull:`10849`).
   By `Stephan Hoyer <https://github.com/shoyer>`_.
+- Add :py:func:`nunique` reduction function (:issue:`9548`), which behaves like
+  :py:func:`pandas.DataFrame.nunique` applied along specific dimensions.
+  By `Ewan Short <https://github.com/eshort0401>`_.
+
 
 Breaking Changes
 ~~~~~~~~~~~~~~~~