numpy · math-hiyoko · Apr 15, 2025 · Apr 16, 2025 · Apr 16, 2025 · Apr 16, 2025
diff --git a/doc/release/upcoming_changes/28767.change.rst b/doc/release/upcoming_changes/28767.change.rst
@@ -0,0 +1,10 @@
+``unique_values`` for string dtypes may return unsorted data
+------------------------------------------------------------
+np.unique now supports hash‐based duplicate removal for string dtypes.
+This enhancement extends the hash-table algorithm to byte strings ('S'),
+Unicode strings ('U'), and the experimental string dtype ('T', StringDType).
+As a result, calling np.unique() on an array of strings will use
+the faster hash-based method to obtain unique values.
+Note that this hash-based method does not guarantee that the returned unique values will be sorted.
+This also works for StringDType arrays containing None (missing values)
+when using equal_nan=True (treating missing values as equal).
diff --git a/doc/release/upcoming_changes/28767.performance.rst b/doc/release/upcoming_changes/28767.performance.rst
@@ -0,0 +1,10 @@
+Performance improvements to ``np.unique`` for string dtypes
+-----------------------------------------------------------
+The hash-based algorithm for unique extraction provides
+an order-of-magnitude speedup on large string arrays. 
+In an internal benchmark with about 1 billion string elements,
+the hash-based np.unique completed in roughly 35.1 seconds,
+compared to 498 seconds with the sort-based method
+– about 14× faster for unsorted unique operations on strings.
+This improvement greatly reduces the time to find unique values
+in very large string datasets.
diff --git a/numpy/_core/src/multiarray/multiarraymodule.c b/numpy/_core/src/multiarray/multiarraymodule.c
@@ -4572,7 +4572,7 @@ static struct PyMethodDef array_module_methods[] = {
     {"from_dlpack", (PyCFunction)from_dlpack,
         METH_FASTCALL | METH_KEYWORDS, NULL},
     {"_unique_hash",  (PyCFunction)array__unique_hash,
-        METH_O, "Collect unique values via a hash map."},
+        METH_FASTCALL | METH_KEYWORDS, "Collect unique values via a hash map."},
     {NULL, NULL, 0, NULL}                /* sentinel */
 };