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
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