On Thu, 2006-10-05 at 15:44 -0700, Kaom Te wrote:> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Hello,
>
> I'm a novice user trying to figure out how to retain NA aggregate
> values. For example, given a data frame with data for 3 of the 4
> possible factor colors("orange" is omitted from the data frame),
I want
> to calculate the average height by color, but I'd like to retain the
> knowledge that "orange" is a possible factor, its just missing.
Here is
> the example code:
>
> > data <- data.frame(color =
factor(c("blue","red","red","green","blue"),
> levels =
c("blue","red","green","orange")),
> height = c(2,8,4,4,5))
> > aggregate(data$height, list(color = data$color), mean)
> color x
> 1 blue 3.5
> 2 red 6.0
> 3 green 4.0
> >
>
> Instead I would like to get
>
> color x
> 1 blue 3.5
> 2 red 6.0
> 3 green 4.0
> 4 orange NA
>
> Is this possible. I've read as much documentation as I can find, but am
> unable to find the solution. It seems like something people would need
> to do. So I would assume it must be built in somewhere or do I need to
> write my own version of aggregate?
>
> Thanks in advance,
> Kaom
If you review the Details section of ?aggregate, you will note:
"Empty subsets are removed, ..."
Thus, one approach is:
tmp <- tapply(data$height, data$color, mean, na.rm = TRUE)
> tmp
blue red green orange
3.5 6.0 4.0 NA
DF <- data.frame(color = names(tmp), mean.height = tmp,
row.names = seq(along = tmp))
> DF
color mean.height
1 blue 3.5
2 red 6.0
3 green 4.0
4 orange NA
HTH,
Marc Schwartz