Compact Vector Replication // Replicates vectors using ALTREP (Alternative Representations for R Objects), avoiding unnecessary memory allocation. When a vector is repeated many times, only a reference to the original data is stored rather than copying the full expanded replicates into memory. The expanded data is only materialised if it is modified, making repeated vectors cheap to create and pass around. This is particularly useful when working with large repeated sequences, such as replicated index vectors, simulation inputs, or repeated reference values in data pipelines.