Patent ID: 8560528

Claim:
A computer-implemented method comprising: accessing an item list that includes one or more items that have been rated by a user; and creating and storing a sketch of the item list, the sketch being a data structure storing a concise description of the item list, wherein creating each sketch includes: selecting a hash function from a plurality of hash functions of a type; using the hash function to generate a permutation of the item list, the permutation including a plurality of hashed values, each of the plurality of hashed values corresponding to at least one item in the item list; storing a minimum value of the permutation in the sketch, the minimum value being a minimum of the plurality of hashed values; repeatedly generating other permutations of the item list, using other hash functions selected from the plurality of hash functions of the type; storing other minimum values of the other permutations in the sketch; and storing item ratings in the sketch such that there is one stored item rating associated with each stored minimum value, the one stored item rating being a rating, made by the user, associated with an item represented by the stored minimum value.