WordNet sense 1 (an operation that segregates items into groups according to a specified criterion):

sorting

WordNet sense 2 (a category of things distinguished by some common characteristic or quality):

form, kind, variety

WordNet sense 3 (examine in order to test suitability):

screen, sieve, screen out

WordNet sense 4 (arrange or order by classes or categories):

assort, class, classify, separate, separate, sort out