[R] Using table to get frequencies of several factors at once

[S Ellison]

You could use a variant of apply(), probably sapply

For example
d <- as.data.frame( matrix(sample(0:1, 200, replace=TRUE), ncol=5))

head(d)

sapply(d, table)

S Ellison
> -----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
> 1 Fouché Street
> Windhoek West
> Windhoek
> Namibia
>  
> Tel:   +264 61 419 000
> Fax:  +264 61 419 001/2
> Mob: +264 81 4456 286
> 
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