Odp: Problem with retrieving updated variables after attach()

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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