reference to objects

Thanks for your answer,
Yes, that will create two copies.  What is it you want to do with the data?
Do you want the capability of both of them changing the data?  What type of
processing are you going to do?
The data should be read only (and all the objects share the same data values).
One way is to store the 'name' of the object in the location and then use
'get/assign' to reference the data:

obj1$dist <- 'dist'
obj2$dist <- 'dist'

my.sum <- sum(get(obj1$data))
assign(obj1$data, new.values)
The problem with this solution is that I would like to use those objects with
already existing libraries, and thus I cannot choose how the data is read.
To explain better, I look for a way to reference to the data that is transparent
to the application.

In C this would be done by assigning the pointer to the data structure, for example
if dist is a C structure and obj1/2 contain a pointer called dist to that kind of
structure, I would do:

obj1->dist = &dist;
obj2->dist = &dist;

and then the rest of the code would not even know if obj1->dist is shared among different
objects....

Thanks again,
Giampiero

__________________________________________________________
James Holtman        "What is the problem you are trying to solve?"
Executive Consultant  --  Office of Technology, Convergys
james.holtman at convergys.com
+1 (513) 723-2929

                      Giampiero Salvi
                      <giampi at speech.kth.se        To:       r-help at stat.math.ethz.ch
                      >                            cc:
                      Sent by:                     Subject:  [R] reference to objects
                      r-help-bounces at stat.m
                      ath.ethz.ch

                      01/16/2004 08:22

Hi,
is there a way to reference to a data object without copying it?

For example I have a huge matrix called dist and I want two objects
obj1 and obj2 to have a memeber dist that points to the matrix, but
I don't want, for memory reasons, to copy the matrix twice.

As far as I understand the following code will generate three copies
of my data:

dist <- some_code_that_generates_data
obj1$dist <- dist
obj2$dist <- dist

Thank you!
Giampiero

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://www.stat.math.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html

--
"NOTICE:  The information contained in this electronic mail transmission is
intended by Convergys Corporation for the use of the named individual or
entity to which it is directed and may contain information that is
privileged or otherwise confidential.  If you have received this electronic
mail transmission in error, please delete it from your system without
copying or forwarding it, and notify the sender of the error by reply email
or by telephone (collect), so that the sender's address records can be
corrected."

On Fri, 16 Jan 2004, Giampiero Salvi wrote (in reply to some unidentified
helper):
Thanks for your answer,

Yes, that will create two copies.  What is it you want to do with the data?
Do you want the capability of both of them changing the data?  What type of
processing are you going to do?
The data should be read only (and all the objects share the same data values).
If the data are read only it is likely that R will *not* create two
copies, eg try
  a<-list(x=rnorm(1e6))
  gc()
  b<-a$x
  d<-a$x
  gc()
  b<-b+1
  d<-d+1
  gc()

One way is to store the 'name' of the object in the location and then use
'get/assign' to reference the data:

obj1$dist <- 'dist'
obj2$dist <- 'dist'

my.sum <- sum(get(obj1$data))
assign(obj1$data, new.values)

This won't work any better.  get(obj1$data) will get the object, and
there's no reason to expect that it's less likely to get a copy than
simple assignment is.

	-thomas