Pairs of similar objects in a population of objects can be found using a process that includes identifying a comparison vector x in a set of vectors having non-zero features, determining an estimated similarity contribution of a subset of features of the comparison vector x to a similarity between the comparison vector x and each vector in the set of vectors, generating an index that includes features based on a comparison of the similarity contribution with a similarity threshold, and identifying another vector in the set that is similar to the vector x using the index.