We investigate the self-assembly of polydisperse polyelectrolyte-amphiphile complexes (PACs) on the basal plane of highly ordered pyrolytic graphite (HOPG) at submonolayer coverage. The PACs assemble as straight rods that organize into raftlike structures on the surface. We find length self-sorting of PACs in the rafts such that each PAC neighbors preferably a PAC of similar length on each side. We show that the observed length segregation can be explained by pairwise interactions.