1. A method for recording the inclusion frequency of an element over a plurality of sets, the method comprising: a) maintaining one or more maps of one or more spaces, wherein each of said maps includes one or more items that uniquely span each of said spaces; b) obtaining a target element from an input set; c) identifying one of said maps of one of said spaces, wherein said target element is associated with said space; d) mapping said target element onto one of said items in said identified map; e) incrementing a count that is associated with the mapped item; f) storing a set identifier in association with the mapped item, wherein said identifier identifies said input set that includes said mapped target element; and repeating steps b)-f) for a plurality of elements in a plurality (N) of input sets, wherein each of said elements is mapped only once.