Are approximation algorithms for consensus clustering worthwhile?

Consensus clustering has emerged as one of the principal clustering problems in the data mining community. In recent years the theoretical computer science community has generated a number of approximation algorithms for consensus clustering and similar problems. These algorithms run in polynomial time, with performance guaranteed to be at most a certain factor worse than optimal. We investigate the feasibility of the approximation algorithms, in an attempt to link data-mining and theoretical research. On realistic data sets, algorithms with quadratic running times are impractical. Unfortunately these and even worse running times are typical of approximation algorithms. To circumvent this, we sample from the data, run the “slow” algorithms on the sample, and then build a consensus clustering from the seed sample clustering, using a range of techniques. These unsampling techniques are in fact almost as good at creating consensus partitionings as the approximation and data-mining algorithms themselves. We find that one of the latest approximation algorithms is not only fast and effective, but also easy to describe, making it an ideal choice.