Abstract: A system can provide unique user metrics associated with a node in a hierarchy and the node's decedents in real time. This can occur by merging sketches of the node and its decedents to form a merged sketch, and retrieving the unique user metrics from the merged sketch. The sketches and the merged sketch may each be a separate data form, such as a hash. The hierarchy may include an online content taxonomy and the sketches of each node may include unique user metrics associated with the node, such as user interaction metrics associated with a category of content of the node. The system may build sketches for the nodes of a hierarchy, associate each sketch with its ancestor sketches, invert the associations, tie corresponding descendant sketches of an ancestor sketch based on the inversions, and merge the descendant sketches with their ancestor sketches to generate the merged sketches.