[R] Levels number of a factor object

[Laurent Houdusse]

Hi all!

    How to retrieve the levels number of a factor object?
    See this code:
    groups<-gl(4,10)
    I want to retrieve the number of levels (4) of my object "groups"
    I tried groups.levels but this don't work

    Thanks


Laurent Houdusse 
Analyste Programmeur