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, wherein the updating circuit partially updates the users' features when the update ratio is less than the pre-defined threshold ratio, the pre-defined threshold ratio being configurable based on a preference of the existing sparse matrix factorization, and wherein, when the number of changed ratings of the sparse matrix factorization greater than the pre-defined threshold ratio, the updating circuit partially updates the users' features only if the new content rating occur in a sub-group of the users, and a sub-group of the items at a rate greater than a threshold value.