[R] qby -- Quietly repeat Stata command on subsets of the data
qby varlist: command
qby varlist1 [(varlist2)] [, sort rc0]: command
qbys varlist: command
qbys varlist1 [(varlist2)] [, rc0]: command
qby and qbys are convenience commands and are equivalent to
quietly by ...
quietly bysort ...
See by and quietly.