Methods, systems, and devices are described for wireless communication. In one aspect, a method of wireless communication includes selecting, by a wireless device, a first subset from a first set of candidate multi-user groups of stations. The first subset is based at least in part on first-level grouping metrics associated with the first set of candidate multi-user groups. The method further includes determining second-level grouping metrics associated with a second set of candidate multi-user groups. The second set corresponds to candidate multi-user groups having a greater number of stations or channel vectors than the first set, and the second set is based at least in part on the first subset.