a vector of clusterings. Zero elements mean that the sample was absent
during clustering
Details
Connectivity matrix (M) is a binary matrix N-by-N
M[i,j] = 1 if sample i and j are in the same cluster
ref: Monti et al. (2003) "Consensus Clustering: A Resampling-Based Method for
Class Discovery and Visualization of Gene Expression Microarray Data", Machine Learning