1. A computer-implemented method comprising: receiving, from a viewing user of a social networking system, a request for stories describing one or more actions of one or more users of the social networking system; identifying one or more users of the social networking system connected to the viewing user; obtaining interaction data describing one or more actions performed by the one or more users connected to the viewing user on one or more objects associated with the social networking system; generating an aggregated story unit from the interaction data, the aggregated story unit including two or more content items associated with a common characteristic and identifying a plurality of actions performed by the one or more users connected to the viewing user; determining, based on one more input selection policies, whether to include in the aggregated story unit: (1) an input element associated with a collection of all of the content items included in the aggregated story unit, or (2) an input element associated with each individual content item included in the aggregated story unit, wherein an input selection policy is based at least in part on prior user interactions with other aggregated story units including other content items associated with the same common characteristic as the content items included in the aggregated story unit; and providing, for display to the viewing user, the aggregated story unit with one or more input elements based on the determining.