1. An alternating least square recommendation system comprising: a receiving circuit configured to receive an existing sparse matrix factorization saved in a data store to incrementally update factorized features when users change ratings of content of the existing sparse matrix factorization; and an updating circuit configured to determine an update ratio based on a number of changed ratings of the sparse matrix factorization and to update the users' features by using the existing content ratings of the existing sparse matrix factorization if the update ratio is less than a pre-defined threshold ratio.