verbose("Generating a new reference set");
List<SparseDoubleVector> vectors =
new ArrayList<SparseDoubleVector>();
// Assume that data is sparse.
MatrixBuilder builder = new ClutoSparseMatrixBuilder();
for (int i = 0; i < rows; ++i) {
int cols = minValues.length;
// If the average number of values per row is significantly
// smaller than the total number of columns then select a subset