[R] Factor levels.

[Peter Dalgaard]

Rolf Turner wrote:
>     P.S.  ***Are*** there any risks/dangers in following Christos 
> Hatzis' suggestion of simply doing
>
>             levels(fff) <- c("U","A","S")       ???
Not if the levels are right to begin with.

Problems only arise if fff somehow becomes a two-level factor, e.g. if 
you do
   fff <- fff[2:3, drop=TRUE].
Then you can get this effect:

 >  fff
[1] Unit        Scholarship Scholarship Unit      
Levels: Scholarship Unit
 > fff[2:3, drop=TRUE]
[1] Scholarship Scholarship
Levels: Scholarship
 > fff[-(2:3), drop=TRUE]
[1] Unit Unit
Levels: Unit
 > ggg <- fff[2:3, drop=TRUE]
 > levels(ggg) <- c("a","b")
 > ggg
[1] a a
Levels: a b
 > ggg <- fff[-(2:3), drop=TRUE]
 > levels(ggg) <- c("a","b")
 > ggg
[1] a a
Levels: a b


-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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