Add Python bindings for get_json_object (#7981)

Fixes: [7916](#7916)

Authors:
  - Sheilah Kirui (https://github.com/skirui-source)

Approvers:
  - Keith Kraus (https://github.com/kkraus14)

URL: #7981

python/cudf/cudf/_lib/cpp/strings/json.pxd

@@ -0,0 +1,16 @@
+# Copyright (c) 2021, NVIDIA CORPORATION.
+
+from cudf._lib.cpp.column.column_view cimport column_view
+from cudf._lib.cpp.scalar.scalar cimport string_scalar
+from libcpp.memory cimport unique_ptr
+from libcpp.string cimport string
+
+from cudf._lib.cpp.column.column cimport column
+from cudf._lib.cpp.scalar.scalar cimport scalar
+
+
+cdef extern from "cudf/strings/json.hpp" namespace "cudf::strings" nogil:
+    cdef unique_ptr[column] get_json_object(
+        column_view col,
+        string_scalar json_path,
+    ) except +

python/cudf/cudf/_lib/strings/json.pyx

@@ -0,0 +1,36 @@
+# Copyright (c) 2021, NVIDIA CORPORATION.
+
+from libcpp.memory cimport unique_ptr
+from libcpp.utility cimport move
+from cudf._lib.cpp.column.column_view cimport column_view
+from cudf._lib.cpp.scalar.scalar cimport string_scalar
+from cudf._lib.cpp.types cimport size_type
+from cudf._lib.column cimport Column
+from cudf._lib.scalar cimport DeviceScalar
+from cudf._lib.cpp.column.column cimport column
+
+from cudf._lib.cpp.strings.json cimport (
+    get_json_object as cpp_get_json_object
+)
+
+
+def get_json_object(Column col, object py_json_path):
+    """
+    Apply a JSONPath string to all rows in an input column
+    of json strings.
+    """
+    cdef unique_ptr[column] c_result
+
+    cdef column_view col_view = col.view()
+    cdef DeviceScalar json_path = py_json_path.device_value
+
+    cdef const string_scalar* scalar_json_path = <const string_scalar*>(
+        json_path.get_raw_ptr()
+    )
+    with nogil:
+        c_result = move(cpp_get_json_object(
+            col_view,
+            scalar_json_path[0],
+        ))
+
+    return Column.from_unique_ptr(move(c_result))

python/cudf/cudf/core/column/string.py

@@ -110,6 +110,7 @@
     startswith_multiple as cpp_startswith_multiple,
 )
 from cudf._lib.strings.findall import findall as cpp_findall
+from cudf._lib.strings.json import get_json_object as cpp_get_json_object
 from cudf._lib.strings.padding import (
     PadSide,
     center as cpp_center,
@@ -2180,6 +2181,72 @@ def get(self, i: int = 0) -> ParentType:
 
         return self._return_or_inplace(cpp_string_get(self._column, i))
 
+    def get_json_object(self, json_path):
+        """
+        Applies a JSONPath string to an input strings column
+        where each row in the column is a valid json string
+
+        Parameters
+        ----------
+        json_path: str
+            The JSONPath string to be applied to each row
+            of the input column
+
+        Returns
+        -------
+        Column: New strings column containing the retrieved json object strings
+
+        Examples
+        --------
+        >>> import cudf
+        >>> s = cudf.Series(
+            [
+                \"\"\"
+                {
+                    "store":{
+                        "book":[
+                            {
+                                "category":"reference",
+                                "author":"Nigel Rees",
+                                "title":"Sayings of the Century",
+                                "price":8.95
+                            },
+                            {
+                                "category":"fiction",
+                                "author":"Evelyn Waugh",
+                                "title":"Sword of Honour",
+                                "price":12.99
+                            }
+                        ]
+                    }
+                }
+                \"\"\"
+            ])
+        >>> s
+            0    {"store": {\n        "book": [\n        { "cat...
+            dtype: object
+        >>> s.str.get_json_object("$.store.book")
+            0    [\n        { "category": "reference",\n       ...
+            dtype: object
+        """
+
+        try:
+            res = self._return_or_inplace(
+                cpp_get_json_object(
+                    self._column, cudf.Scalar(json_path, "str")
+                )
+            )
+        except RuntimeError as e:
+            matches = (
+                "Unrecognized JSONPath operator",
+                "Invalid empty name in JSONPath query string",
+            )
+            if any(match in str(e) for match in matches):
+                raise ValueError("JSONPath value not found") from e
+            raise
+        else:
+            return res
+
     def split(
         self, pat: str = None, n: int = -1, expand: bool = None
     ) -> ParentType:

python/cudf/cudf/tests/test_string.py

@@ -1,5 +1,6 @@
 # Copyright (c) 2018-2021, NVIDIA CORPORATION.
 
+import json
 import re
 import urllib.parse
 from contextlib import ExitStack as does_not_raise
@@ -2932,6 +2933,145 @@ def test_string_slice_with_mask():
     assert_eq(actual, expected)
 
 
+@pytest.mark.parametrize(
+    "data",
+    [
+        [
+            """
+            {
+                "store":{
+                    "book":[
+                        {
+                            "category":"reference",
+                            "author":"Nigel Rees",
+                            "title":"Sayings of the Century",
+                            "price":8.95
+                        },
+                        {
+                            "category":"fiction",
+                            "author":"Evelyn Waugh",
+                            "title":"Sword of Honour",
+                            "price":12.99
+                        }
+                    ]
+                }
+            }
+            """
+        ],
+        [
+            """
+            {
+                "store":{
+                    "book":[
+                        {
+                            "category":"reference",
+                            "author":"Nigel Rees",
+                            "title":"Sayings of the Century",
+                            "price":8.95
+                        }
+                    ]
+                }
+            }
+            """,
+            """
+            {
+                "store":{
+                    "book":[
+                        {
+                            "category":"fiction",
+                            "author":"Evelyn Waugh",
+                            "title":"Sword of Honour",
+                            "price":12.99
+                        }
+                    ]
+                }
+            }
+            """,
+        ],
+    ],
+)
+def test_string_get_json_object_n(data):
+    gs = cudf.Series(data)
+    ps = pd.Series(data)
+
+    assert_eq(
+        json.loads(gs.str.get_json_object("$.store")[0]),
+        ps.apply(lambda x: json.loads(x)["store"])[0],
+    )
+    assert_eq(
+        json.loads(gs.str.get_json_object("$.store.book")[0]),
+        ps.apply(lambda x: json.loads(x)["store"]["book"])[0],
+    )
+    assert_eq(
+        gs.str.get_json_object("$.store.book[0].category"),
+        ps.apply(lambda x: json.loads(x)["store"]["book"][0]["category"]),
+    )
+
+
+@pytest.mark.parametrize(
+    "json_path", ["$.store", "$.store.book", "$.store.book[*].category", " "]
+)
+def test_string_get_json_object_empty_json_strings(json_path):
+    gs = cudf.Series(
+        [
+            """
+            {
+                "":{
+                    "":[
+                        {
+                            "":"",
+                            "":"",
+                            "":""
+                        },
+                        {
+                            "":"fiction",
+                            "":"",
+                            "title":""
+                        }
+                    ]
+                }
+            }
+            """
+        ]
+    )
+
+    got = gs.str.get_json_object(json_path)
+    expect = cudf.Series([None], dtype="object")
+
+    assert_eq(got, expect)
+
+
+@pytest.mark.parametrize("json_path", ["a", ".", "/.store"])
+def test_string_get_json_object_invalid_JSONPath(json_path):
+    gs = cudf.Series(
+        [
+            """
+            {
+                "store":{
+                    "book":[
+                        {
+                            "category":"reference",
+                            "author":"Nigel Rees",
+                            "title":"Sayings of the Century",
+                            "price":8.95
+                        },
+                        {
+                            "category":"fiction",
+                            "author":"Evelyn Waugh",
+                            "title":"Sword of Honour",
+                            "price":12.99
+                        }
+                    ]
+                }
+            }
+            """
+        ]
+    )
+
+    with pytest.raises(ValueError):
+        gs.str.get_json_object(json_path)
+
+
 def test_str_join_lists_error():
     sr = cudf.Series([["a", "a"], ["b"], ["c"]])