[R] Why can't this function be used with the 'by' command?

[R. Michael Weylandt]

I believe it has to do with passing multiple columns to the
shapiro.test. Note that

by(x[,1:2], x$group, function(x) shapiro.test(x)[[2]])

doesn't work but

by(x[,1:2], x$group, function(x) shapiro.test(x[,1])[[2]])

does.

Michael

On Thu, Nov 3, 2011 at 8:08 AM, Kaiyin Zhong <kindlychung at gmail.com> wrote:
> Why can't this function be used with the 'by' command?
>
>> x = array(runif(16), dim=c(8,2))
>> x = data.frame(x)
>> x$group = rep(c('wt', 'app'), each=4)
>
>> shapiro.p = function(x) shapiro.test(x)[[2]]
>> apply(x[,1:2], 2, shapiro.p)
>       X1        X2
> 0.4126345 0.2208781
>
>> by(x[,1:2], x$group, shapiro.p)
> Error in `[.data.frame`(x, complete.cases(x)) :
>  undefined columns selected
>
>        [[alternative HTML version deleted]]
>
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