filter_prop_zero        Filter Genes for by Max Proportion Zero Among
                        Groups
get_prop_zero           Get the Proportion of Zero Counts for Each Gene
                        in Each Group
rank_cells              Get the Rank of the Expression for each Gene in
                        each Cell
rank_group              Get the Rank of the Mean expression for each
                        Gene in each Group
rank_invariance         Calculate the Rank Invariance of Each Gene from
                        Cell and Group Ranks
rank_invariance_express
                        Calculate the Rank Invariance of Each Gene from
                        SCE object
sce_zero_test           Test SummarizedExperiment data
