From wvenable@arcola.stats.adelaide.edu.au  Thu Apr 22 04:45:26 1999
From: wvenable@arcola.stats.adelaide.edu.au (wvenable@arcola.stats.adelaide.edu.au)
Date: Thu, 22 Apr 1999 05:45:26 +0200 (MET DST)
Subject: Assigning to a list within a loop (PR#175)
Message-ID: <199904220345.FAA28639@pubhealth.ku.dk>

We noticed this bug in more complex code, but this succinctly
describes the phenomenon.

If you do not re-initialize a each time in the following loop,
the final value only is assigned to all places when the loop is
complete.

> a <- b <- list()
> for(i in 1:5) {
+	a$alpha <- i
+	b[[i]] <- a
+	}
> unlist(b)
alpha alpha alpha alpha alpha 
    5     5     5     5     5 

If a is re-created each time, however the correct behaviour
happens:


> b <- list()
> for(i in 1:5) {
+	  a <- list(alpha = i)
+	  b[[i]] <- a
+	  }
> unlist(b)
alpha alpha alpha alpha alpha 
    1     2     3     4     5 

> version
           _                 
platform   i586-unknown-linux
arch       i586              
os         linux             
system     i586, linux       
status                       
status.rev 0                 
major      0                 
minor      64.0              
year       1999              
month      April             
day        8                 
language   R                 
>

Bill Venables & Berwin Turlach.

-- 
-----------------------------------------------------------------
Bill Venables, Statistician, CMIS Environmetrics Project.

Physical address:                            Postal address:
CSIRO Marine Laboratories,                   PO Box 120,       
233 Middle St, Cleveland, Queensland         Cleveland, Qld, 4163
AUSTRALIA                                    AUSTRALIA

Telephone: +61 7 3826 7251     Email: Bill.Venables@cmis.csiro.au     
      Fax: +61 7 3826 7304

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-devel-request@stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._


Assigning to a list within a loop (PR#175)
wvenable@arcola.stats.adelaide.edu.au