drop_na_at              Drop missing values at columns that match a
                        given pattern
drop_na_if              Conditon based dropping of columns with missing
                        values
get_na_counts           Add columnwise/groupwise counts of missing
                        values
percent_missing         Columnwise missingness percentages
recode_as_na            Recode a value as NA
recode_as_na_for        Recode Values as NA if they meet defined
                        criteria
recode_na_as            Replace missing values with another value
recode_na_if            Recode NA as another value with some conditions
sort_by_missingness     Sort Variables according to missingness
