1. A method comprising: identifying a comparison vector x, identifying a set of candidate vectors corresponding to x; and for each candidate vector y in the set of candidate vectors corresponding to x and a list of similar pairs of vectors: determining, using one or more computers, a similarity estimate between the comparison vector x and the candidate vector y, where the similarity estimate is based on: a sum of a similarity between a set of processed features of the comparison vector x and a set of processed features of the candidate vector y, and a product of a minimum size of at least one of the candidate vector x or a set of non-processed features of the candidate vector y, and a similarity score between a maximum weight of the comparison vector x and a maximum weight of the candidate vector y; if the similarity estimate meets a similarity threshold, determining a similarity score between the comparison vector x and the candidate vector y; and if the similarity score meets the similarity threshold, including a pair of vectors comprising the comparison vector x and the candidate vector y in the list of similar pairs of vectors.