Add optional column_order in JSON reader

cpp/include/cudf/io/json.hpp

@@ -53,6 +53,69 @@ struct schema_element {
    * @brief Allows specifying this column's child columns target type
    */
   std::map<std::string, schema_element> child_types;
+  // // Add constructors for schema_element to keep order too with initializer list.
+  // // templated constructor with schema_element<bool keep_order=false>
+  // // store the order as
+  /** @brief Allows specifying the order of the columns
+   */
+  std::optional<std::vector<std::string>> column_order;
+
+  /**
+   * @brief Default constructor
+   *
+   * @param type The type that this column should be converted to
+   * @param child_types Allows specifying this column's child columns target type
+   * @param column_order Allows specifying the order of the columns
+   */
+  schema_element(data_type type,
+                 std::map<std::string, schema_element> child_types,
+                 std::optional<std::vector<std::string>> column_order = std::nullopt)
+    : type{std::move(type)},
+      child_types{std::move(child_types)},
+      column_order{std::move(column_order)}
+  {
+  }
+
+  /**
+   * @brief Constructor to create a schema_element from a data_type
+   *
+   * @param type The type that this column should be converted to
+   */
+  schema_element(data_type type) : schema_element{type, {}, std::nullopt} {}
+  schema_element() = default;
+  /**
+   * @brief Constructor to create a schema_element with a specific order of columns
+   *
+   * @param type The type that this column should be converted to
+   * @param child_types Allows specifying this column's child columns target type and
+   * the order of the columns
+   */
+  schema_element(data_type type,
+                 std::initializer_list<std::pair<const std::string, schema_element>> child_types)
+    : type{type}
+  {
+    this->column_order->reserve(child_types.size());
+    for (auto const& [key, value] : child_types) {
+      this->column_order->push_back(key);
+    }
+    this->child_types = {std::move(child_types)};
+  }
+
+  schema_element(schema_element const&)     = default;  ///< Copy constructor
+  schema_element(schema_element&&) noexcept = default;  ///< Copy assignment operator
+  /**
+   * @brief Copy assignment operator
+   *
+   * @return Reference to this object
+   */
+  schema_element& operator=(schema_element const&) = default;
+  /**
+   * @brief Move assignment operator
+   *
+   * @return Reference to this object (after transferring ownership)
+   */
+  schema_element& operator=(schema_element&&) noexcept = default;
+  ~schema_element()                                    = default;
 };
 
 /**

cpp/src/io/json/parser_features.cpp

@@ -32,7 +32,7 @@ std::optional<schema_element> child_schema_element(std::string const& col_name,
       [col_name](std::vector<data_type> const& user_dtypes) -> std::optional<schema_element> {
         auto column_index = atol(col_name.data());
         return (static_cast<std::size_t>(column_index) < user_dtypes.size())
-                 ? std::optional<schema_element>{{user_dtypes[column_index]}}
+                 ? std::optional<schema_element>{user_dtypes[column_index]}
                  : std::optional<schema_element>{};
       },
       [col_name](

cpp/tests/io/json/json_test.cpp

@@ -350,7 +350,8 @@ TEST_P(JsonReaderParamTest, JsonLinesStrings)
 
   cudf::io::json_reader_options in_options =
     cudf::io::json_reader_options::builder(cudf::io::source_info{data.data(), data.size()})
-      .dtypes({{"2", dtype<cudf::string_view>()}, {"0", dtype<int32_t>()}, {"1", dtype<double>()}})
+      .dtypes(std::map<std::string, data_type>{
+        {"2", dtype<cudf::string_view>()}, {"0", dtype<int32_t>()}, {"1", dtype<double>()}})
       .lines(true);
 
   cudf::io::table_with_metadata result = cudf::io::read_json(in_options);