Implement __setitem__ for StructColumn (#8737)

Closes #8558

Authors:
  - https://github.com/shaneding

Approvers:
  - Ashwin Srinath (https://github.com/shwina)
  - https://github.com/brandon-b-miller

URL: #8737

python/cudf/cudf/_lib/scalar.pyx

@@ -326,7 +326,7 @@ cdef _set_struct_from_pydict(unique_ptr[scalar]& s,
     else:
         pyarrow_table = pa.Table.from_arrays(
             [
-                pa.array([], from_pandas=True, type=f.type)
+                pa.array([cudf.NA], from_pandas=True, type=f.type)
                 for f in arrow_schema
             ],
             names=columns

python/cudf/cudf/core/column/struct.py

@@ -89,6 +89,15 @@ def __getitem__(self, args):
             }
         return result
 
+    def __setitem__(self, key, value):
+        if isinstance(value, dict):
+            # filling in fields not in dict
+            for field in self.dtype.fields:
+                value[field] = value.get(field, cudf.NA)
+
+            value = cudf.Scalar(value, self.dtype)
+        super().__setitem__(key, value)
+
     def copy(self, deep=True):
         result = super().copy(deep=deep)
         if deep:

python/cudf/cudf/core/indexing.py

@@ -111,10 +111,13 @@ def __setitem__(self, key, value):
         if is_scalar(value):
             value = to_cudf_compatible_scalar(value)
         elif not (
-            isinstance(value, list)
-            and isinstance(self._sr._column.dtype, cudf.ListDtype)
+            isinstance(value, (list, dict))
+            and isinstance(
+                self._sr._column.dtype, (cudf.ListDtype, cudf.StructDtype)
+            )
         ):
             value = column.as_column(value)
+
         if (
             not isinstance(
                 self._sr._column.dtype,

python/cudf/cudf/core/scalar.py

@@ -133,15 +133,13 @@ def _preprocess_host_value(self, value, dtype):
                 return NA, dtype
 
         if isinstance(value, dict):
-            if dtype is not None:
-                raise TypeError("dict may not be cast to a different dtype")
-            else:
+            if dtype is None:
                 dtype = StructDtype.from_arrow(
                     pa.infer_type([value], from_pandas=True)
                 )
-                return value, dtype
+            return value, dtype
         elif isinstance(dtype, StructDtype):
-            if value is not None:
+            if value not in {None, NA}:
                 raise ValueError(f"Can not coerce {value} to StructDType")
             else:
                 return NA, dtype

python/cudf/cudf/core/series.py

@@ -1238,6 +1238,7 @@ def __repr__(self):
                 preprocess._column, cudf.core.column.CategoricalColumn
             )
             and not is_list_dtype(preprocess.dtype)
+            and not is_struct_dtype(preprocess.dtype)
             and not is_decimal_dtype(preprocess.dtype)
         ) or isinstance(
             preprocess._column, cudf.core.column.timedelta.TimeDeltaColumn

python/cudf/cudf/tests/test_struct.py

@@ -101,6 +101,51 @@ def test_struct_getitem(series, expected):
     assert sr[0] == expected
 
 
+@pytest.mark.parametrize(
+    "data, item",
+    [
+        (
+            [
+                {"a": "Hello world", "b": []},
+                {"a": "CUDF", "b": [1, 2, 3], "c": cudf.NA},
+                {"a": "abcde", "b": [4, 5, 6], "c": 9},
+            ],
+            {"a": "Hello world", "b": [], "c": cudf.NA},
+        ),
+        (
+            [
+                {"a": "Hello world", "b": []},
+                {"a": "CUDF", "b": [1, 2, 3], "c": cudf.NA},
+                {"a": "abcde", "b": [4, 5, 6], "c": 9},
+            ],
+            {},
+        ),
+        (
+            [
+                {"a": "Hello world", "b": []},
+                {"a": "CUDF", "b": [1, 2, 3], "c": cudf.NA},
+                {"a": "abcde", "b": [4, 5, 6], "c": 9},
+            ],
+            cudf.NA,
+        ),
+        (
+            [
+                {"a": "Hello world", "b": []},
+                {"a": "CUDF", "b": [1, 2, 3], "c": cudf.NA},
+                {"a": "abcde", "b": [4, 5, 6], "c": 9},
+            ],
+            {"a": "Second element", "b": [1, 2], "c": 1000},
+        ),
+    ],
+)
+def test_struct_setitem(data, item):
+    sr = cudf.Series(data)
+    sr[1] = item
+    data[1] = item
+    expected = cudf.Series(data)
+    assert sr.to_arrow() == expected.to_arrow()
+
+
 @pytest.mark.parametrize(
     "data",
     [