levels() counter-intuitif? (PR#1693)

[rjvbertin@hotmail.com]

Suppose I have a factor size with levels "small", "medium" and "large". 
Then, when I subset this factor:
>ss<-size[size!="medium"]
to get at the extremes,
>levels(ss)
....
Levels:  large medium small

The same happens with
>subset( size, size!="medium")

I understand that the resulting factor inherits the possible levels from its 
"parent", but I do not see in what that is useful. Intuitively, I would 
expect that levels(ss) return "small" and "large". For subset(), there might 
be an option to request inheritance of the number of levels.

RenE J.V. Bertin
College de France/LPPA
11, place Marcelin Berthelot
75005 Paris, France

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