Partitioning of tumor and normal tissues for colon cancer data. Illustration of the tumor and normal tissues after re-ordering the tissues for OREO, Alon et al., nsNMF after sorting of the first and second basis genes (as denoted by nsNMF F1 and nsNMF F2, respectively), hierarchical clustering after optimally re-ordering the leaves (HC (opt)), and hierarchical clustering (HC). In the data matrix, the white elements denote normal tissues and the black elements denote tumor tissues. Only OREO and Alon et al. were successful in separating the normal and tumor tissues into two dense regions.