A method for recommendation of a content item, comprising: providing first identifiers for first content items stored on a first device; providing second identifiers for second content items stored on a second device; determining measures for at least a part of said first content items, wherein each measure is associated with a respective content item, and said measure depends on said first and second identifiers; determining or updating, on a third device, an item-to-item matrix based on said measures, wherein said first, second, and third devices are physically separated devices; determining a recommendation for a user based on said item-to-item matrix.