R devel - Aug 2018 - glm Argument-Evaluation Does Not Match Documentation.

Details in documentation: "All of ?weights?, ?subset?, ?offset?, ?etastart?
and ?mustart? are evaluated in the same way as variables in ?formula?, that is
first in ?data? and then in the environment of ?formula?."
In fact, `data` is usually not an environment, and I have not seen arguments
evaluated in `environment(formula)` when `data` is provided. (Information in
`environment(formula)` is used, so presumably they are evaluated in an
environment whose parent is `environment(formula)`.)


R --vanilla

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> environment(glm)
<environment: namespace:stats>
> maintainer('stats')
[1] "R Core Team <R-core at
r-project.org>"
> df <- data.frame(x=1:3, y=c(pi,7,sqrt(2)), z=c(1,2.3,3))
> a <- 4:6; b <- 7:9
> lm <- glm(z ~ x+y, data=df, weights = a*b -> v)
> v # Check whether weights was evaluated in .GlobalEnv, the environment of
the formula.
Error: object 'v' not found
> env.df <- as.environment(df); lm <- glm(z ~ x+y, data=env.df, weights
= a*b -> v)
Error in list(z, x, y) : could not find function
"list"
> parent.env(env.df) <- .GlobalEnv; lm <- glm(z ~ x+y, data=env.df,
weights = a*b -> v)
> v
Error: object 'v' not found
> ls(env.df) # show that weights was evaluated in env.df
[1] "v" "x" "y" "z"


Suggested rewrite: "All of ?weights?, ?subset?, ?offset?, ?etastart? and
?mustart? are evaluated in the same way as variables in ?formula?. Values needed
are found first in `data` and then usually in the environment of ?formula? &
its ancestors. (If `data` is provided but is not an environment then expressions
are evaluated in an environment with content taken from `data` whose parent is
`environment(formula)`.) Side effects of evaluating the arguments will usually
NOT occur in the caller's frame."
I think this is correct, but what really happens is inside other functions with
unusual argument evaluation, so I'm not certain.


Regards,
Jorgen Harmse
 
Sam?s Club Technology
Phone 512.633.2226 
jorgen.harmse at samsclub.com
 
 
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