add_child	add_child
assign_attr	assign_attr
children_sort	children_sort
create_nodes	create_nodes
create_tree	create_tree
cumsum_across_level	cumsum_across_level
cumsum_by_level	cumsum_by_level
exercise_df	exercise_df
fill_NA_level	fill_NA_level
fixnames	fixnames
fix_items	fix_items
pre_get_array	pre_get_array
test_df	test_df
