[R] how to count "associated" factors?

[Dimitris Rizopoulos]

try this:

X  <- factor(sample(c("A", "B", "C"), 10, TRUE), levels = c("A", "B", 
"C"))
Y  <- factor(sample(c("A", "B", "C"), 10, TRUE), levels = c("A", "B", 
"C"))
#############
table(X, Y)


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/336899
Fax: +32/16/337015
Web: http://www.med.kuleuven.be/biostat/
     http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "zhihua li" <lzhtom at hotmail.com>
To: <r-help at stat.math.ethz.ch>
Sent: Tuesday, June 21, 2005 2:46 PM
Subject: [R] how to count "associated" factors?


> hi netters
>
> Suppose I have a factor X, with 10 elements and 3 levels: A B B C A 
> C B A C
> C .
>
> It is easy to count the number of elements for each level:
> tapply(X,X,length).
>
> Now I have another factor Y, which formed a matrix with X:
>
> X| A B B C A C B A C C
> Y| B B C C C A A A B B
>
> I wanna count the number of elements for each of these conditions: 
> when X=A
> and Y=A; when X=A and Y=B; when X=A and Y=C; when X=B and Y=A; when 
> X=B and
> Y=B; when X=B and Y=C; when X=C and Y=A; when X=C and Y=B; when X=C 
> and
> Y=C.
>
> The code I have written for this task is too complicated, involving 
> a lot
> of for loops and if conditions. I believe there's some nice code 
> that can
> do it far more efficiently. Can anyone give me a hint?
>
> Thanks a lot!
>
>


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