R help - Dec 2010 - 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

It seems to be dependent upon the the character ("assigned
alphabetically") which I found out by manually changing the order of
appearance of the characters in rfactor; the colour would stick to the character
"a", whether this appears first in rfactor or not.

I as able to control the colours being used by
> boxplot(x~rfactor, col=c("2", "6",
"3","5","4"))
Rgds,
Rainer

Disclaimer:
I'm new to R and very early on the learning curve - just trying my best...


On Saturday 04 December 2010 01:22:56 Eduardo Klein
wrote:
> 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 <eklein <at> usb.ve> writes:

> I would like to know how R assigns the numeric code to a set of factors 
> in a vector. 
  [snip]
> 
  It is indeed alphabetical by default.  To get it in order of
appearance you could do something like

set.seed(1001)
x <- sample(letters[1:5],50,replace=TRUE)
f <- factor(x,levels=unique(x))