[R] how to count "associated" factors?

From: zhihua li <lzhtom_at_hotmail.com>
Date: Tue 21 Jun 2005 - 22:46:25 EST

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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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Jun 21 22:56:57 2005

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