[R] how to include 'NA's in xtabs?
Sundar Dorai-Raj
sundar.dorai-raj at pdf.com
Wed May 14 22:49:38 CEST 2003
Kosenkov Kirill wrote:
> Hello!
>
> I have a dataset with NA's in some variables (factors), for example:
> $ P67 : Factor w/ 2 levels "-","+": NA 2 1 NA NA 2 1 1 2 NA ...
>
The key is here. Should be 3 levels if you want NAs included.
> I need to use 'xtabs' like
> xtabs(~x$P67)
> It works well and produces something like this:
> x$P67
> - +
> 779 1318
> but i want to compute NA's too, like this:
> x$P67
> - + NA
> 779 1318 137
>
> I am trying xtabs(~x$P67, exclude=NULL) but xtabs does not compute 'NA's
> in this case too.
>
> I do not want to transform my data (do not want to do any substitution
> on NA's).
>
> How i can say 'xtabs' to compute NA-values?
>
> and second question: how to use argument 'na.action' in 'xtabs'?
> 'xtabs' help page does not explain this.
>
> Thanks!
>
Try this:
x$P67 = factor(x$P67, exclude = NULL)
xtabs(~x$P67)
Here's an example:
R> x = factor(c(1:2, NA), exclude = NULL, labels = c("+", "-", "0"))
R> xtabs(~ x)
x
+ - 0
1 1 1
Sundar
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