[R] Keeping factors with zero occurrences in "table" output

[Liaw, Andy]

If you make them into factors, the empty ones should show up:

> f1 <- sample(1:7, 10, replace=TRUE)
> f2 <- sample(1:6, 10, replace=TRUE)
> table(f1, f2)
   f2
f1  1 2 3 5 6
  1 0 0 1 0 0
  2 0 0 1 0 0
  3 0 0 2 1 0
  4 0 1 0 0 1
  5 1 1 0 0 0
  7 0 0 0 1 0
> ff1 <- factor(f1, levels=1:7)
> ff2 <- factor(f2, levels=1:7)
> table(ff1, ff2)
   ff2
ff1 1 2 3 4 5 6 7
  1 0 0 1 0 0 0 0
  2 0 0 1 0 0 0 0
  3 0 0 2 0 1 0 0
  4 0 1 0 0 0 1 0
  5 1 1 0 0 0 0 0
  6 0 0 0 0 0 0 0
  7 0 0 0 0 1 0 0

HTH,
Andy

> From: Ravi Varadhan
> 
> Dear R group,
> 
>  
> 
> I have a data frame which contains data on preferences on 7 
> items (ranks 1
> through 7) listed by each participant.  I would like to 
> tabulate this in a
> 7x7 table where the rows would be the items and the columns 
> would be the
> number of times that item received a particular rank.  
> 
>  
> 
> I tried doing this by creating a matrix by "rbind"ing each 
> vector obtained
> using "table" on each item.  This, however, does not work 
> because there are
> some items which didn't receive some of the ranks, so "table" 
> does not list
> that item.  Is there a way to force it to list the item and 
> give a "0" to
> it? Or, is there a simpler way to solve this problem?
> 
>  
> 
> Thanks for any help,
> 
> Ravi.
> 
>  
> 
> --------------------------------------------------------------
> ------------
> 
> Ravi Varadhan, Ph.D.
> 
> Assistant Professor,  The Center on Aging and Health
> 
> Division of Geriatric Medicine and Gerontology
> 
> Johns Hopkins University
> 
> Ph: (410) 502-2619
> 
> Fax: (410) 614-9625
> 
> Email:   <mailto:rvaradhan at jhmi.edu> rvaradhan at jhmi.edu
> 
> --------------------------------------------------------------
> ------------
> 
>  
> 
> 
> 	[[alternative HTML version deleted]]
> 
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