Dear Minghua Yao, I suggest you looking up the archives of the mailing list. The answers to the following message made things clear to me: Wayne Jones <JonesW at kssg.com> Címzett: R-Help <R-help at stat.math.ethz.ch> Tárgy: [R] Sorting a data frame Dátum: Wed, 16 Jul 2003 14:42:09 +0100 Gábor