[R] Cross tabulation with fixed dimensions

[David Winsemius]

On Mar 5, 2010, at 11:43 AM, Tarmo Remmel wrote:

> Hello,
>
> This is a seemingly simple task, but it has been frustrating me for  
> too
> long, so I am turning to this list for some help.
>
> I have two vectors of factors which are quite long; two simple  
> examples are
> shown here:

No, those are not "factors" in the R sense... but they _should_ be:

 > a <- factor(c(1,2,3,4,5), levels=1:6)
 > b <- factor(c(1,2,5,5,6), levels=1:6)
 >
 > tab <- table(a,b)
 > tab
    b
a   1 2 3 4 5 6
   1 1 0 0 0 0 0
   2 0 1 0 0 0 0
   3 0 0 0 0 1 0
   4 0 0 0 0 1 0
   5 0 0 0 0 0 1
   6 0 0 0 0 0 0

>
>> a <- c(1,2,3,4,5)
>> b <- c(1,2,5,5,6)
>
> If I produce a cross-tabulation of these vectors, I get the following:
>
>> tab <- table(a,b)
>
>> table(a,b)
>   b
> a   1 2 5 6
>  1 1 0 0 0
>  2 0 1 0 0
>  3 0 0 1 0
>  4 0 0 1 0
>  5 0 0 0 1
>
> I really want to have this cross-tabulation expanded to include all  
> factors
> present in the input data.  Thus, I need additional columns for  
> categories 3
> and 4, and a row for category 6, albeit, they will be filled with  
> zeros.  Is
> there an easy way of doing this?
>
> Thanks,
>
> Tarmo
>
>
>
> ____________________________________________
> Tarmo K. Remmel Ph.D.
> Assistant Professor, Department of Geography
> York University, N413A Ross Building
> Toronto, Ontario, M3J 1P3, Canada
> Tel: 416-736-2100 x22496; Fax: 416-736-5988
> http://www.yorku.ca/remmelt
> Skype: tarmoremmel
>
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> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT