[R] Constructing an environment from a data.frame

[Uwe Ligges]

Duncan Murdoch wrote:

> Code like
> 
> df <- data.frame(x=1:10)
> y <- 20:29
> 
> eval(quote(x+y), env=df)
> 
> does what you might expect:  it looks for x and y in the data.frame,
> and when it doesn't find y there, it looks in the parent environment.
> 
> However, sometimes I'd like to construct a single environment out of
> df, so that I can pass it to nested functions and get the same
> behaviour.  Right now, I get the wrong answer from code like this:
> 
> f1 <- function(df) {
>     g <- function() {
> 	eval(quote(x+y), env=df)
>     }
>     y <- 1:10
>     g()
> }
> 
> f1(df)
> 
> because the eval looks in the environment of f1, finds y there, and
> gives me the wrong answer.
> 
> I can modify f1 so it works:
> 
> f2 <- function(df) {
>     g <- function(env) {
> 	eval(quote(x+y), env=df, enclos=env)
>     }
>     y <- 1:10
>     g(parent.frame())
> }
> 
> but this means carrying around both parent.frame() and df.  I'd like
> to do this:
> 
> f3 <- function(df) {
>     env <- as.environment(df)
> 
>     g <- function() {
> 	eval(quote(x+y), env=env)
>     }
> 
>     y <- 1:10
>     g()
> }
> 
> and get the same result as from f2(df), but currently as.environment
> doesn't like to be passed a data.frame.  Is there a better way to do
> the same thing?
> 
> Duncan Murdoch


I don't think it's easily possibe (but Luke et al. might want to correct 
me). My dirty solution would be:

f4 <- function(df) {
     env <- new.env()
     mapply(function(x, y) assign(y, x, envir=env), df, names(df))
     g <- function()
         eval(quote(x+y), env=env)
     y <- 1:10
     g()
}
f4(df)



Uwe