An image array includes pixels, each representing an image-based feature value of a patient obtained from imaging. The array includes first and second dimensions. Pixels corresponding to a specific patient of a plurality of patients extend in the first dimension and pixels corresponding to a specific feature of a plurality of features extend in the second dimension. Patients represented in the image array are grouped into two or more groups. Each indicates a known condition, such that patients having a first and second conditions are respectively part of a first and a second group and are in a first and a second portion of the array, respectively. The groups are separately organized according to a selected feature. Patients of the first and second groups are respectively arranged in an order of values for the selected feature within the first and second portions.