Calculating Unique Social Networking System Users Performing An Action On A Social Networking System Object

A social networking system generates one or more metrics describing user interactions with objects to describe the popularity of the objects among users. Data describing actions performed by social networking system users on objects stored by the social networking system to identify an action, the user performing the action and the object on which the action was performed. Stored actions performed on a selected object are retrieved and a subset of the actions is generated by sampling the stored actions at a sampling rate. A number of unique users included in the subset is determined and used along with the sampling rate to determine the number of unique users included in the retrieved actions, which is used to derive a metric describing user interaction with the selected object.