caculate the frequencies of the Amino Acids

may some one please help me to sort this out, i am trying to writ a  
R code
for calculating the frequencies of the amino acids in 9 different  
sequences,
i want the code to read the sequence from external text file, i used  
the
following code to do so:
x<-read.table("sequence.txt",header=FALSE)

then i defined an array for 20 amino acids as following:
AA<- 
c 
('A 
','C 
','D 
','E','F','G','H','I','K','L','M','N','P','Q','R','S','T','V','W','Y')
i am using the following code to calculate the frequencies:

frequency<-function(X)
{
y<-rep(0,20)
for(j in 1:nchar(as.character(x$V1[i]))){

for(i in 1:9){

	res<-which(AA==substr(x$V1[i],j,j))

	y[res]=y[res]+1
	}
	}
return(y)
}

but this code actually is not working, it reads only one sequence, i  
dont
know why the loop is not working for the "i", which suppose to read  
the nine
rows of the file sequence.txt. the sequence.txt file is attached to  
this
message.

cheers
http://n4.nabble.com/file/n997072/sequence.txt sequence.txt
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