Using table to get frequencies of several factors at once

-----Original Message-----
From: r-help-bounces at r-project.org 
[mailto:r-help-bounces at r-project.org] On Behalf Of Pancho Mulongeni
Sent: 11 January 2013 11:18
To: R help
Subject: [R] Using table to get frequencies of several factors at once

Hi, I have a dataframe with n columns, but I am only looking 
at five of them. And lots of rows, over 700. 
So I would like to find frequencies for each of the numeric 
columns (variables) using the table function. However, is 
there a fast way to produce a frequency table where the 5 
rows represent the 5 numeric variables and the columns refer 
to the values (levels) of the respective numeric variables, 
which in this case are 0 and 1.  
The only way I have figured it out is via a for loop:
m<-seq(218,222,1) #these are columns of the variables in the 
larger dataframe tm<-m[1:5] #I need this for the for loop
l.tm<-length(tm)
B<-matrix(nrow=l.tm,ncol=2)  #the matrix to hold the freqs 
for (p in 1:l.tm) { var.num<-m[p]
B[p,]<-table(DATA[,var.num])
}

B

     [,1] [,2]
[1,]  697    9
[2,]  512  194
[3,]  604  102
[4,]  700    6
[5,]  706  706
So the rows represent my five variables (columns) that occupy 
columns 218 through 222 in the DATA dataframe.
So the second column represents my frequencies of the value 
1, which is what I am interested in. The last row has a 
double entry, because there was only one value, 0, with a 
freq of 706 and so R duplicated in the two columns, but 
that's ok, I can just ignore it. 

So is there are better way to do this? Is there a way to use 
the so called tapply function? I struggle to understand the 
help doc for this.function.


Pancho Mulongeni
Research Assistant
PharmAccess Foundation
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