The group actions in Particle Flow let you identify and act on subsets of particles, specified either explicitly or procedurally according to any of a number of different conditions. You can create as many groups as you like, and apply any event’s actions to any group.
The Group Operator applies an entire event to the particles specified by one or more . The Group Operator is useful when you want to apply an event to a subset of particles, but you don't want to split the particles from the current event. It affects the selected particles only while they remain in the current event.
The Group Selection operator extends Particle Flow's ability to select particles. Originally in Particle Flow, you select a single group of particles explicitly that remains selected throughout the entire flow. With Group Selection, however, you can specify any number of groups according to various criteria: location, particle properties, at random, and more.