[R] MASS::boxcox "object not found"

[Jeff Newmiller]

It is rarely a good idea to invoke lm without providing the inputs in a 
data frame through the data argument. In this case, just making that 
change is insufficient though... the boxcox.lm function calls the update 
function, which re-retreives the data in a new context. The workaround is 
to supply the data= argument to boxplot which will pass it on to the 
update function to keep the data visible in the updated lm model.  None of 
this seemed obvious to me from the boxplot help, but I think I would 
regard using the data= argument to boxplot as being about as essential as 
it is in lm, because the alternative is to assume that all the data are 
as-named in the global environment (x is different than vec).

#######
library(MASS)
bc <- function(vec) {
    dta <- data.frame( vec = vec ) # Rarely a good idea to call "lm"
                                   # without the data argument.
    model <- lm( vec ~ 1, data = dta )
    lam <- boxcox( model, data=dta )
    lam <- lam$x[which.max(lam$y)]
    (vec^lam - 1)/lam
}
x <- runif(20)
bc(x)

#' ![](https://i.imgur.com/lhKymfQ.png)

#'     #>  [1] -0.92115159 -0.21776512 -1.20946708 -0.16700312 -0.76096811
#'     #>  [6] -0.12208801 -0.61723623 -0.78302973 -0.62455538 -1.40636663
#'     #> [11] -0.52627869 -0.09377700 -1.02867887 -0.68288810 -0.93872856
#'     #> [16] -0.17005783 -0.01754519 -0.83549564 -0.35399612 -1.34878425

#' Created on 2018-08-06 by the [reprex package](http://reprex.tidyverse.org) (v0.2.0).

#######

On Sun, 5 Aug 2018, Jinsong Zhao wrote:

> Hi there,
>
> I wrote a function that wraps MASS::boxcox as:
>
> bc <- function(vec) {
>   lam <- boxcox(lm(vec ~ 1))
>   lam <- lam$x[which.max(lam$y)]
>   (vec^lam - 1)/lam
> }
>
> When I invoke it as:
>
>> x <- runif(20)
>> bc(x)
> Error in eval(predvars, data, env) : object 'vec' not found
>
> I have googled, and rewrote the above function as:
>
> bc <- function(vec) {
>   dat <<- data.frame(vec = vec)
>   lam <- boxcox(lm(vec ~ 1, dat))
>   lam <- lam$x[which.max(lam$y)]
>   rm(dat, envir = .GlobalEnv)
>   (vec^lam - 1)/lam
> }
>
> It works. But, I am wondering why MASS::boxcox have to wrap in such way that have to use the data in .GlobalEnv.
>
> Best,
> Jinsong
> 	[[alternative HTML version deleted]]
>
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>

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