When I run yy <- ddply(all,"ACTIVIT", summarise, mode=mode(COUNTS)) I get : ACTIVIT mode XX numeric ZZ numeric & so on. -- View this message in context: http://r.789695.n4.nabble.com/Can-package-plyr-also-calculate-the-mode-tp4663235p4663349.html Sent from the R help mailing list archive at Nabble.com.