  We numerically demonstrate bidirectional sorting of flocking particles
interacting with an array of asymmetric barriers. Each particle aligns with the
average swimming direction of its neighbors according to the Vicsek model and
experiences additional steric interactions as well as repulsion from the fixed
barriers. We show that particles preferentially localize to one side of the
barrier array over time, and that the direction of this rectification can be
reversed by adjusting the particle-particle exclusion radius or the noise term
in the equations of motion. These results provide a conceptual basis for
isolation and sorting of single- and multi-cellular organisms which move
collectively according to flocking-type interaction rules.
