How do you work with the largest five, or smallest five, or any other fixed number of values in a tail of a distribution? In this column, I give examples of problems and code for basic calculations as a prelude to graphics, tables, and more detailed analysis. The main illustration is analysis of concentration among firms or companies, with wider discussion mentioning hydrology, climatology, cryptography, and ecology. The examples allow a tutorial covering sorting and ranking and using if and in to select observations, by: as a framework for groupwise calculations, indicator variables as a mode of selection, and egen as a Swiss Army knife with many handy functions.