  Among ensemble clustering methods, Evidence Accumulation Clustering is one of
the simplest technics. In this approach, a co-association (CA) matrix
representing the co-clustering frequency is built and then clustered to extract
consensus clusters. Compared to other approaches, this one is simple as there
is no need to find matches between clusters obtained from two different
partitionings. Nevertheless, this method suffers from computational issues, as
it requires to compute and store a matrix of size n x n, where n is the number
of items. Due to the quadratic cost, this approach is reserved for small
datasets. This work describes a trick which mimic the behavior of average
linkage clustering. We found a way of computing efficiently the density of a
partitioning, reducing the cost from a quadratic to linear complexity.
Additionally, we proved that the k-means maximizes naturally the density. We
performed experiments on several benchmark datasets where we compared the
k-means and the bisecting version to other state-of-the-art consensus
algorithms. The k-means results are comparable to the best state of the art in
terms of NMI while keeping the computational cost low. Additionally, the
k-means led to the best results in terms of density. These results provide
evidence that consensus clustering can be solved with simple algorithms.
