R devel - Aug 2001 - R 1.3.0 bug: after "y _ 10; x[[1]] _ y", assigning to "y[1]" modifies "x" (PR#1043)

After a list element has been assigned from a vector variable,
assigments to elements of the original vector variable modify the copy
stored in the list as well.

Here's a transcript illustrating the problem:

        R : Copyright 2001, The R Development Core Team
        Version 1.3.0  (2001-06-22)

        [ . . . ]

        > x _ list()
        > y _ 10
        > x[[1]] _ y
        > x
        [[1]]
        [1] 10

        > y[1] _ 20   # should only modify "y"
        > x
        [[1]]
        [1] 20        # ACK!  we modified "x", too

        > 

Kevin <buhr@stat.wisc.edu>

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buhr@stat.wisc.edu writes:
> After a list element has been assigned from a vector variable,
> assigments to elements of the original vector variable modify the copy
> stored in the list as well.
> 
> Here's a transcript illustrating the problem:
> 
>         R : Copyright 2001, The R Development Core Team
>         Version 1.3.0  (2001-06-22)
> 
>         [ . . . ]
> 
>         > x _ list()
>         > y _ 10
>         > x[[1]] _ y
>         > x
>         [[1]]
>         [1] 10
> 
>         > y[1] _ 20   # should only modify "y"
>         > x
>         [[1]]
>         [1] 20        # ACK!  we modified "x", too
> 
>         > 
> 
> Kevin <buhr@stat.wisc.edu>
Confirmed with 1.3.0-patched on RedHat 7.1. For easier reproduction:

x <- list()
y <- 10
x[[1]] <- y
x
y[1] <- 20   # should only modify "y"
# y <- 20 # Works OK with this instead
x
 


-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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