1. A method comprising: storing, in a memory location, a plurality of media sets for a community of users; and preprocessing, using a processor, the plurality of media sets to quantify an association between pairs of media items, comprising: for each item in a mediaset, identifying every other item in the same mediaset, so as to define all of the pairs of media items in that mediaset; repeating said identifying step for every other mediaset in the plurality of media sets, thereby defining every pair of items that appears in any mediaset in the plurality of media sets; for each identified pair of media items, adjusting a concurrency metric value responsive to each additional occurrence of the same pair of items in the plurality of media sets; storing media library collection data for a plurality of user accounts; receiving, from a client device, information about at least one input media item; identifying a candidate set of media items by selecting media having an adjusted concurrency value over a predetermined threshold value and containing the at least one input media item; accessing the user account associated with the client device; and filtering the candidate set based on the media library collection data for the user of the client device.