add_child               Add children node
assign_attr             assign attributes to node; work with fix_items
                        function
children_sort           Sort chidren nodes with certain order
create_nodes            create a tree with assigned name, children and
                        fields
create_tree             create tree appended with each element of input
                        list as a child
cumsum_across_level     cumulative calculation
cumsum_by_level         calculate cumsum for input level
exercise_df             Anonymized sample exercise data
fill_NA_level           fill missing value of a field across a level
                        with 0
fix_items               assign certain children nodes and fill NA for
                        empty fields
fixnames                numericalize children numeric name to convert
                        JSON object to JSON array
pre_get_array           numericalize children numeric name to convert
                        JSON object to JSON array
test_df                 Anonymized sample data
