Using table to get frequencies of several factors at once

-----Original Message-----
From: p.mulongeni at namibia.pharmaccess.org
Sent: Fri, 11 Jan 2013 11:17:42 +0000
To: r-help at r-project.org
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
1 Fouch? Street
Windhoek West
Windhoek
Namibia

Tel:?? +264 61 419 000
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