1. A system comprising: one or more computers; and a non-transitory computer-readable medium coupled to the one or more computers having instructions stored thereon which, when executed by the one or more computers, cause the one or more computers to perform operations comprising: obtaining a vector that represents a particular user; applying k locality sensitive hash functions to each component of the vector to generate a set of k hash values, wherein k is an integer parameter, and wherein applying k locality sensitive hash functions to each component of the vector comprises, for each of the k hash values, applying, quantity b times, k locality sensitive hash functions to each component of the vector, wherein b represents a bit length of the hash value; and assigning the particular user to k clusters, each of which is represented by a respective corresponding one of the k hash values.