[R] Problem with xtabs(), exclude=NULL, and counting NA's

[David Winsemius]

On Sep 24, 2009, at 10:06 AM, hadley wickham wrote:

>> wtf <- factor(x, levels(c(levels(wtf), NA), exclude=NULL)
>> xtabs (~ wtf, exclude=NULL, na.action=na.pass)
>
> Also see addNA.
>

That is nice. The addNA function does not exactly jump off the page  
for the (too) casual reader. In the context of the OP's original  
problem, these lines of code are illustrative:

 > xtabs(~addNA(wkhp), x, exclude=NULL, na.action=na.pass)
addNA(wkhp)
   20   30   40   45   60 <NA>
    1    1   10    1    3    4
 > x$wtf <- cut(x$wkhp, breaks=seq(20, 80, by=20) )
 > xtabs( ~ addNA(wkhp), x)
addNA(wkhp)
   20   30   40   45   60 <NA>
    1    1   10    1    3    4
 > xtabs( ~ addNA(wtf), x)
addNA(wtf)
(20,40] (40,60] (60,80]    <NA>
      11       4       0       5

> Hadley
>
>
> -- 
> http://had.co.nz/

David Winsemius, MD
Heritage Laboratories
West Hartford, CT