Add memory_usage & items implementation for Struct column & dty…

…pe (#12033)

Fixes: #11893 

- [x] This PR implements `StructColumn.memory_usage` and `StructDtype.items`

Authors:
  - GALI PREM SAGAR (https://github.com/galipremsagar)

Approvers:
  - Lawrence Mitchell (https://github.com/wence-)

URL: #12033

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

@@ -1,6 +1,8 @@
 # Copyright (c) 2020-2022, NVIDIA CORPORATION.
 from __future__ import annotations
 
+from functools import cached_property
+
 import pandas as pd
 import pyarrow as pa
 
@@ -65,6 +67,17 @@ def to_pandas(self, index: pd.Index = None, **kwargs) -> "pd.Series":
             pd_series.index = index
         return pd_series
 
+    @cached_property
+    def memory_usage(self):
+        n = 0
+        if self.nullable:
+            n += cudf._lib.null_mask.bitmask_allocation_size_bytes(self.size)
+
+        for child in self.children:
+            n += child.memory_usage
+
+        return n
+
     def element_indexing(self, index: int):
         result = super().element_indexing(index)
         return {

python/cudf/cudf/core/dtypes.py

@@ -4,6 +4,7 @@
 import operator
 import pickle
 import textwrap
+from functools import cached_property
 from typing import Any, Callable, Dict, List, Tuple, Type, Union
 
 import numpy as np
@@ -627,6 +628,13 @@ def deserialize(cls, header: dict, frames: list):
                 fields[k] = pickle.loads(dtype)
         return cls(fields)
 
+    @cached_property
+    def itemsize(self):
+        return sum(
+            cudf.utils.dtypes.cudf_dtype_from_pa_type(field.type).itemsize
+            for field in self._typ
+        )
+
 
 decimal_dtype_template = textwrap.dedent(
     """

python/cudf/cudf/tests/test_list.py

@@ -864,6 +864,8 @@ def test_memory_usage():
     assert s1.memory_usage() == 44
     s2 = cudf.Series([[[[1, 2]]], [[[3, 4]]]])
     assert s2.memory_usage() == 68
+    s3 = cudf.Series([[{"b": 1, "a": 10}, {"b": 2, "a": 100}]])
+    assert s3.memory_usage() == 40
 
 
 @pytest.mark.parametrize(

python/cudf/cudf/tests/test_struct.py

@@ -371,3 +371,24 @@ def test_nested_struct_extract_host_scalars(data, idx, expected):
     series = cudf.Series(data)
 
     assert _nested_na_replace(series[idx]) == _nested_na_replace(expected)
+
+
+def test_struct_memory_usage():
+    s = cudf.Series([{"a": 1, "b": 10}, {"a": 2, "b": 20}, {"a": 3, "b": 30}])
+    df = s.struct.explode()
+
+    assert_eq(s.memory_usage(), df.memory_usage().sum())
+
+
+def test_struct_with_null_memory_usage():
+    df = cudf.DataFrame(
+        {
+            "a": cudf.Series([1, 2, -1, -1, 3], dtype="int64"),
+            "b": cudf.Series([10, 20, -1, -1, 30], dtype="int64"),
+        }
+    )
+    s = df.to_struct()
+    assert s.memory_usage() == 80
+
+    s[2:4] = None
+    assert s.memory_usage() == 272