[R] summaryBy: transformed variable on RHS of formula?

[Gabor Grothendieck]

On Mon, Apr 2, 2012 at 11:58 AM, Alexander Shenkin <ashenkin at ufl.edu> wrote:
> Hi Folks,
>
> I'm trying to cut my data inside the summaryBy function.  Perhaps
> formulas don't work that way?  I'd like to avoid adding another column
> if possible, but if I have to, I have to.  Any ideas?
>
> Thanks,
> Allie
>
>    require(doBy)
>    df = dataframe(a <- rnorm(100), b <-rnorm(100))
>    summaryBy(a ~ cut(b,c(-100,-1,1,100)), data=df) # preferred
> solution, but it throws an error
>                                                    # Error in
> `[.data.frame`(data, , rh.var, drop = FALSE) : undefined columns selected
>
>    df$c = cut(b,c(-100,-1,1,100))
>    summaryBy(a ~ c, data=df)       # works fine
>

Try this:

summaryBy(a ~ b, data = transform(df, b = cut(b, c(-100, -1, 1, 100))))

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