A method includes first determining among a plurality of cells a first set of cells that are anomalous, second determining among remaining cells a second set of cells that are anomalous, and identifying a resulting set of anomalous cells being a combination of the first set and the second set of anomalous cells. The first determining is based on input data of a plurality of first features of each cell among the plurality of cells, and a first machine learning operation. The second determining is based on the input data of the plurality of first features of each cell among the remaining cells, and a second machine learning operation different from the first machine learning operation.