table function in a matrix

Dear Petr,
Thanks for your help. Sorry one more query for one of my datasets which has NAs (missing genotypes). Is there any way in which I can count NAs?
Many thanks!
Sarah

From: Sarah Auburn <sauburn at yahoo.com>
To: Petr Savicky <savicky at cs.cas.cz>
Cc: "r-help at r-project.org" <r-help at r-project.org>
Sent: Thursday, 7 June 2012, 23:24
Subject: Re: [R] table function in a matrix


Perfect, thank you!

From: Petr Savicky <savicky at cs.cas.cz>
To: r-help at r-project.org
Sent: Thursday, 7 June 2012, 19:42
Subject: Re: [R] table function in a matrix

On Wed, Jun 06, 2012 at 11:02:46PM -0700, Sarah Auburn wrote:

Hi,
I am trying to get a summary of the counts of different variables for each sample in a matrix of the form "m" below to generate an output as shown. (Ultimately I want to generate a stacked barchart for each sample). I am only able to get the "table" function to work on one sample (column) at a time. Any help appreciated.
Thank you
Sarah
?
a<-c("A", "A", "B", "B", "C", "A", "C", "D", "A", "D", "C", "A", "D", "C", "A", "C")
m<-matrix(a, nrow=4)
m
???? [,1] [,2] [,3] [,4]
[1,] "A"? "C"? "A"? "D"
[2,] "A"? "A"? "D"? "C"
[3,] "B"? "C"? "C"? "A"
[4,] "B"? "D"? "A"? "C"

output needed (so that I can use the "barplot(t(output))" function):
       A B C D
[,1] 2 2 0 0
[,2] 1 0 2 1
[,3] 2 0 1 1
[,4] 1 0 2 1

Hi.

Try the following.

   a<-c("A", "A", "B", "B", "C", "A", "C", "D", "A", "D", "C", "A", "D", "C", "A", "C")
   m<-matrix(a, nrow=4)
   tab <- function(x) { table(factor(x, levels=LETTERS[1:4])) }
   t(apply(m, 2, tab))

       A B C D
   [1,] 2 2 0 0
   [2,] 1 0 2 1
   [3,] 2 0 1 1
   [4,] 1 0 2 1

Factors are used to ensure that all the tables have the same length,
even if some letters are missing.

Hope this helps.

Petr Savicky.