knowing the code-number of factors in a vector

Hi,

I would like to know how R assigns the numeric code to a set of factors 
in a vector. For example, I have a vector of 5 different factors in a 
random order, and I want a color-coded plot by factors:

rfactor=as.factor(sample(letters[1:5], 50, replace=T))
rfactor
  [1] c c c d b a b d d a a e e b b e c e e a a b b b a b a e a a b d b 
b c a b b
[39] d c a e c d e d a a a a
Levels: a b c d e

x=rnorm(50)
boxplot(x~rfactor, col=1:5)

So, colors 1 to 5 are assigned to factors alphabetically (a-1, b-2, ..., 
e-5), or by order of appearance (c-1, d-2, b-3, a-4, e-5)? It is 
possible to control that?

Saludos, EKS

Eduardo Klein
Lab Sensores Remotos e
Instituto de Tecnolog?a y Ciencias Marinas
Universidad Sim?n Bol?var
Caracas, Venezuela
ph (58) (212) 906-3111 ext 6700
fax (58) (212( 906-3111 ext 6701