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

[Achim Zeileis]

On Wed, 20 Apr 2005 11:38:13 -0400 Ravi Varadhan wrote:

> 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?

I think the cleanest way is to store the preferences as a "factor" and
tell R at the creation of that factor what the levels are, i.e.
  preference <- factor(preference, levels = 1:7)
Then calling
  table(preference)
will also report categories with 0 observations.
Z

 
>  
> 
> 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
> 
> ---------------------------------------------------------------------
> -----
> 
>  
> 
> 
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