diff --git a/python/ray/data/_internal/pandas_block.py b/python/ray/data/_internal/pandas_block.py
index 5bbaff67bb75..03c26781dd1c 100644
--- a/python/ray/data/_internal/pandas_block.py
+++ b/python/ray/data/_internal/pandas_block.py
@@ -429,10 +429,17 @@ def iter_groups() -> Iterator[Tuple[KeyType, Block]]:
                     if next_row is None:
                         next_row = next(iter)
                     next_key = next_row[key]
+                    if type(next_row[key]) is _pandas._libs.missing.NAType:
+                        next_row = next(iter)
+                        continue
+
                     while np.all(next_row[key] == next_key):
                         end += 1
                         try:
                             next_row = next(iter)
+                            if type(next_row[key]) is _pandas._libs.missing.NAType:
+                                next_row = next(iter)
+                                continue
                         except StopIteration:
                             next_row = None
                             break
@@ -520,17 +527,23 @@ def aggregate_combined_blocks(
 
         stats = BlockExecStats.builder()
         keys = key if isinstance(key, list) else [key]
+
         key_fn = (
             (lambda r: tuple(r[r._row.columns[: len(keys)]]))
             if key is not None
             else (lambda r: (0,))
         )
 
-        iter = heapq.merge(
-            *[
-                PandasBlockAccessor(block).iter_rows(public_row_format=False)
-                for block in blocks
-            ],
+        iterables = [
+            filter(
+                lambda r: tuple(r[r._row.columns[: len(keys)]])[0] is not None,
+                PandasBlockAccessor(block).iter_rows(public_row_format=False),
+            )
+            for block in blocks
+        ]
+
+        iters = heapq.merge(
+            *iterables,
             key=key_fn,
         )
         next_row = None
@@ -538,19 +551,20 @@ def aggregate_combined_blocks(
         while True:
             try:
                 if next_row is None:
-                    next_row = next(iter)
+                    next_row = next(iters)
+
                 next_keys = key_fn(next_row)
                 next_key_names = (
                     next_row._row.columns[: len(keys)] if key is not None else None
                 )
 
                 def gen():
-                    nonlocal iter
+                    nonlocal iters
                     nonlocal next_row
                     while key_fn(next_row) == next_keys:
                         yield next_row
                         try:
-                            next_row = next(iter)
+                            next_row = next(iters)
                         except StopIteration:
                             next_row = None
                             break
diff --git a/python/ray/data/_internal/planner/exchange/sort_task_spec.py b/python/ray/data/_internal/planner/exchange/sort_task_spec.py
index 0a2910f2fa34..5124870cc490 100644
--- a/python/ray/data/_internal/planner/exchange/sort_task_spec.py
+++ b/python/ray/data/_internal/planner/exchange/sort_task_spec.py
@@ -1,6 +1,7 @@
 from typing import List, Tuple, TypeVar, Union
 
 import numpy as np
+import pandas as pd
 
 from ray.data._internal.delegating_block_builder import DelegatingBlockBuilder
 from ray.data._internal.planner.exchange.interfaces import ExchangeTaskSpec
@@ -105,6 +106,18 @@ def sample_boundaries(
         samples = builder.build()
 
         sample_dict = BlockAccessor.for_block(samples).to_numpy(columns=columns)
+
+        for k, v in sample_dict.items():
+            if v.dtype == object:
+                sample_dict[k] = np.array(
+                    [
+                        i
+                        for i in v
+                        if i is not None and type(i) is not pd._libs.missing.NAType
+                    ],
+                    dtype=object,
+                )
+
         # Compute sorted indices of the samples. In np.lexsort last key is the
         # primary key hence have to reverse the order.
         indices = np.lexsort(list(reversed(list(sample_dict.values()))))
diff --git a/python/ray/data/_internal/util.py b/python/ray/data/_internal/util.py
index e07cbc238ec2..e0b4384a904f 100644
--- a/python/ray/data/_internal/util.py
+++ b/python/ray/data/_internal/util.py
@@ -51,11 +51,9 @@
 _LOCAL_SCHEME = "local"
 _EXAMPLE_SCHEME = "example"
 
-
 LazyModule = Union[None, bool, ModuleType]
 _pyarrow_dataset: LazyModule = None
 
-
 cached_cluster_resources = {}
 cluster_resources_last_fetch_time = 0
 CLUSTER_RESOURCES_FETCH_INTERVAL_SECONDS = 10
@@ -735,6 +733,7 @@ def find_partition_index(
             return right
         col_name = columns[i]
         col_vals = table[col_name].to_numpy()[left:right]
+        col_vals = [x for x in col_vals if x is not None]
         desired_val = desired[i]
 
         prevleft = left
@@ -990,7 +989,8 @@ def call_with_retry(
                 # Retry with binary expoential backoff with random jitter.
                 backoff = min((2 ** (i + 1)) * random.random(), max_backoff_s)
                 logger.debug(
-                    f"Retrying {i+1} attempts to {description} after {backoff} seconds."
+                    f"Retrying {i + 1} attempts to {description} after "
+                    f"{backoff} seconds."
                 )
                 time.sleep(backoff)
             else:
diff --git a/python/ray/data/tests/test_pandas.py b/python/ray/data/tests/test_pandas.py
index ec27c296a296..8e1205fb88d4 100644
--- a/python/ray/data/tests/test_pandas.py
+++ b/python/ray/data/tests/test_pandas.py
@@ -180,6 +180,25 @@ def test_read_pandas_data_array_column(ray_start_regular_shared):
     assert all(row["array"] == [1, 1, 1])
 
 
+def test_ray_ds_unique(ray_start_regular_shared):
+    items = [1, 2, 3, 2, 3]
+    ds = ray.data.from_items(items)
+    assert ds.unique("item") == [1, 2, 3]
+
+
+def test_ray_ds_unique_with_none(ray_start_regular_shared):
+    items = [1, 2, 3, 2, 3, None, 4, 4, 5, 6, 7, 8, 9, 10, 11, 12, None, None]
+    ds = ray.data.from_items(items)
+    assert ds.unique("item") == [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
+
+
+def test_ray_ds_unique_with_none_from_pandas(ray_start_regular_shared):
+    df = pd.DataFrame({"col": [1, 2, 3, None]}, dtype="Int64")
+    ds = ray.data.from_pandas(df)
+    # ds.unique("col")
+    assert ds.unique("col") == [1, 2, 3]
+
+
 if __name__ == "__main__":
     import sys