Data imputation using a trust network for recommendation via matrix factorization

Disclosed is a missing grade imputation device for imputing a grade on an item which a certain user does not evaluate with grades by neighbor users connected through a reliability network. The missing grade can be imputed through: a step of determining users who can reach a certain user in the forward direction of an edge and users who can reach the certain user in the forward direction of the edge as neighbor users; a step of acquiring grades by the neighbor users on an item which is not graded by the certain user from the grade matrix of the certain user; and a step of imputing the grade on the item which is not graded by the certain user by the certain user from a value calculated from the grades by the neighbor users on the item which is not graded by the certain user.