Fix Groupby.get_group (rapidsai#14728)

Closes rapidsai#14727

Authors:
  - Richard (Rick) Zamora (https://github.com/rjzamora)
  - Charles Blackmon-Luca (https://github.com/charlesbluca)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)
  - Charles Blackmon-Luca (https://github.com/charlesbluca)

URL: rapidsai#14728

python/cudf/cudf/core/groupby/groupby.py

@@ -377,7 +377,7 @@ def get_group(self, name, obj=None):
         if obj is None:
             obj = self.obj
 
-        return obj.loc[self.groups[name]]
+        return obj.loc[self.groups[name].drop_duplicates()]
 
     @_cudf_nvtx_annotate
     def size(self):

python/cudf/cudf/tests/groupby/test_indexing.py

@@ -1 +1,12 @@
-# Copyright (c) 2023, NVIDIA CORPORATION.
+# Copyright (c) 2023-2024, NVIDIA CORPORATION.
+import cudf
+from cudf.testing._utils import assert_eq
+
+
+def test_rank_return_type_compatible_mode():
+    # in compatible mode, rank() always returns floats
+    df = cudf.DataFrame({"a": range(10), "b": [0] * 10}, index=[0] * 10)
+    pdf = df.to_pandas()
+    expect = pdf.groupby("b").get_group(0)
+    result = df.groupby("b").get_group(0)
+    assert_eq(expect, result)