Architecture for handling large data selections with small and substantially constant memory footprints. The architecture facilitates the creation of sets of data objects (e.g., rows) of a data source based on selection of the data objects. The set structures can be defined according to a range (span) of data objects selected and a pattern of the objects selected. These set structures are then saved in memory, rather than the data objects, to provide optimized memory usage. In a database implementation, the solution stores the set representation (the structure) in nearly a constant amount of memory, regardless of the number of rows in the grid, and regardless of the number of rows selected. Memory usage can be proportional to the number of discontinuous spans of rows selected by the user. Structures in memory can be consolidated, replaced, or eliminated dynamically as the user changes row selections and pattern criteria.