Hi,
I have read the previous thread on using references to objects in a
function but the solution suggested does'nt seem to be working.
basically I have an object x which has an attribute a containing some
text. I would like to pass x to a function which will change the
attribute a with some new text and have the change visible when the
function exits.
something like
attr(x,'a') <- 'some text'
f <- function(z) {
attr(z,'a') <- 'some new text'
}
So that when I call f(x)
attr(x,'a')
gives
'some new text'
I went by the example below
g <- function(z) eval(eval(substitute(expression(z[1] <<- z[1]+1))))
a <- 1:5
g(a) # increments first element of a by 1
a # c(2,2,3,4,5)
replcing the innermost bracket with attr(z,'a') <- 'some new
text' but
the the after returning from the function the attribute of x does not
get changed.
Could anybody point out how I could achieve this? Do I need to use the
R.oo package or can this be done without external packages?
Thanks,
-------------------------------------------------------------------
Rajarshi Guha <rxg218 at psu.edu> <http://jijo.cjb.net>
GPG Fingerprint: 0CCA 8EE2 2EEB 25E2 AB04 06F7 1BB9 E634 9B87 56EE
-------------------------------------------------------------------
How I wish I were what I was when I wished I were what I am.
Don't you just need to use return?
x <- 1
attr(x,'a') <- 'some text'
f <- function(z) {
attr(z,'a') <- 'some new text'
return(z)
}
y <- f(x)
y
Rajarshi -
Read help("<-") to see what's going on in the example
from previous emails. In your new function, in addition
to setting attr(z,'a') you will need to assign the
result in the global environment.
However, please think hard about whether the final result
couldn't be achieved in some much more straightforward
manner than setting an attribute on an existing object.
That sounds like asking for trouble down the road.
- tom blackwell - u michigan medical school - ann arbor -
On Tue, 2 Mar 2004, Rajarshi Guha wrote:
> Hi,
> I have read the previous thread on using references to objects in a
> function but the solution suggested does'nt seem to be working.
>
> basically I have an object x which has an attribute a containing some
> text. I would like to pass x to a function which will change the
> attribute a with some new text and have the change visible when the
> function exits.
>
> something like
>
> attr(x,'a') <- 'some text'
> f <- function(z) {
> attr(z,'a') <- 'some new text'
> }
>
> So that when I call f(x)
> attr(x,'a')
>
> gives
>
> 'some new text'
>
> I went by the example below
> g <- function(z) eval(eval(substitute(expression(z[1] <<-
z[1]+1))))
> a <- 1:5
> g(a) # increments first element of a by 1
> a # c(2,2,3,4,5)
>
> replcing the innermost bracket with attr(z,'a') <- 'some new
text' but
> the the after returning from the function the attribute of x does not
> get changed.
>
> Could anybody point out how I could achieve this? Do I need to use the
> R.oo package or can this be done without external packages?
>
> Thanks,
>
> -------------------------------------------------------------------
> Rajarshi Guha <rxg218 at psu.edu> <http://jijo.cjb.net>
> GPG Fingerprint: 0CCA 8EE2 2EEB 25E2 AB04 06F7 1BB9 E634 9B87 56EE
> -------------------------------------------------------------------
> How I wish I were what I was when I wished I were what I am.
>
> ______________________________________________
> 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
>
The double arrow in the example you cite is essential;
you can't leave it out since that's what tells R to
search through its parents' environments:
attr(z,'a') <<- 'some new text'
---
Date: Tue, 02 Mar 2004 16:52:20 -0500
From: Rajarshi Guha <rxg218 at psu.edu>
To: R <r-help at stat.math.ethz.ch>
Subject: [R] using object reference
Hi,
I have read the previous thread on using references to objects in a
function but the solution suggested does'nt seem to be working.
basically I have an object x which has an attribute a containing some
text. I would like to pass x to a function which will change the
attribute a with some new text and have the change visible when the
function exits.
something like
attr(x,'a') <- 'some text'
f <- function(z) {
attr(z,'a') <- 'some new text'
}
So that when I call f(x)
attr(x,'a')
gives
'some new text'
I went by the example below
g <- function(z) eval(eval(substitute(expression(z[1] <<- z[1]+1))))
a <- 1:5
g(a) # increments first element of a by 1
a # c(2,2,3,4,5)
replcing the innermost bracket with attr(z,'a') <- 'some new
text' but
the the after returning from the function the attribute of x does not
get changed.
Could anybody point out how I could achieve this? Do I need to use the
R.oo package or can this be done without external packages?
Thanks,
-------------------------------------------------------------------
Rajarshi Guha <rxg218 at psu.edu> <http://jijo.cjb.net>;
GPG Fingerprint: 0CCA 8EE2 2EEB 25E2 AB04 06F7 1BB9 E634 9B87 56EE
-------------------------------------------------------------------
How I wish I were what I was when I wished I were what I am.