data_preparation        Utility functions for data type conversion
                        between data.frame and list.
geom_venn               Plot venn diagram as a ggplot layer object. It
                        supports only data frame as input.
get_venn_table          Extract Venn diagram data table from ggvenn
                        plot
ggvenn                  Plot venn diagram as an independent function.
                        It supports both data frame and list as input.
