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