[R] knowing the code-number of factors in a vector

[Ivan Calandra]

Hi!

As Ben Bolker told you already, the levels are alphabetically ordered by 
default.
When you print rfactor, the last line shows you the different levels, in 
the saved order.
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                   ## here

If you want to change the order manually, do this:
rfactor=as.factor(sample(letters[1:5], 50, replace=T))
rfactor
  [1] e e a a e a a a b a a d a b a b b c d c b e b e d d c a a e a b c 
e b c b e
[39] a e e d b e c b e d a e   ## different values because of sample()
Levels: a b c d e
rfactor2 <- factor(rfactor, levels=c("e","d","c","b","a"))
rfactor2
  [1] e e a a e a a a b a a d a b a b b c d c b e b e d d c a a e a b c 
e b c b e
[39] a e e d b e c b e d a e  ## but the values here are the same as for 
my rfactor
Levels: e d c b a                  ## note that the order here is the 
one you typed in your call to factor(, levels=)

HTH,
Ivan


Le 12/4/2010 02:04, Rainer Schuermann a écrit :
> 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
>>
>>
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>

-- 
Ivan CALANDRA
PhD Student
University of Hamburg
Biozentrum Grindel und Zoologisches Museum
Abt. Säugetiere
Martin-Luther-King-Platz 3
D-20146 Hamburg, GERMANY
+49(0)40 42838 6231
ivan.calandra at uni-hamburg.de

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