[R] Odp: Problem with retrieving updated variables after attach()

[Petr PIKAL]

Hi


r-help-bounces at r-project.org napsal dne 10.02.2009 12:02:53:

> Hello,
> 
> suppose I have a data frame:
> 
> > mat
>  id age
> 1 NA  NA
> 2 NA  NA
> 3 NA  NA
> 4 NA  NA
> 5 NA  NA
> 
> Then I attach the data frame:
> 
> > attach(mat)

Look into docs what attach does. If you do not understand environments use 
attach with great care

The database is not actually attached. Rather, a new environment is 
created on the search path and the elements of a list (including columns 
of a data frame) or objects in a save file or an environment are copied 
into the new environment. If you use <<- or assign to assign to an 
attached database, you only alter the attached copy, not the original 
object. (Normal assignment will place a modified version in the user's 
workspace: see the examples.) For this reason attach can lead to 
confusion. 


> 
> I assign some new values...
> 
> > id <<- sample(100,5)
> > age <<- rnorm(5,mean=30)
> 
> Then I want to create a new data frame from the variables id and age 
which 
> still are attached to position 2 of the R environment...
> 
> > new_mat <- data.frame(ls(pos=2)) # I want to rescue ALL variables that 
were 
> created by attach(mat)
> 
> > new_mat
>  ls.pos...2.
> 1         age
> 2          id
> 
> But this leads to a bogus object... how can I rescue the updated id and 
age 
> values into new_mat?

What about not using attach and transform mat directly

> mat$age <- rnorm(5,mean=30)
> mat$id <- sample(100,5)
> mat
  id      age
1 24 29.17842
2 88 31.22606
3 32 30.81540
4  5 29.31528
5 11 29.32775

Regards
Petr


> 
> 
> Regards,
> 
> David
> 
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