40. The method of claim 3 in which each vector represents a corresponding document, and each feature of each vector represents a frequency with which a word appears in the document.
3. A method comprising: for each vector v in a dataset and a list of similar pairs of vectors: identifying v as a comparison vector; identifying a set of candidate vectors corresponding to v; for each candidate vector w in the set of candidate vectors corresponding to v: determining by operation of one or more computers a similarity estimate between the comparison vector v and the candidate vector w; if the similarity estimate meets a similarity threshold, determining a similarity score between the comparison vector v and the candidate vector w; and if the similarity score meets the similarity threshold, including a pair of vectors comprising the comparison vector v and the candidate vector w in the list of similar pairs of vectors.