R-alpha: Assingment to list or vector elements

[Martyn Plummer]

When you assign a value to an object which exists in some database on
the search list, R creates a copy in the current environment. However,
if the object is a list or vector, and you assign a new value to one of
its elements, a copy is not made and the assignment fails (with no error
message!).  This behaviour is incompatible with S-PLUS, which will make
a copy of the object before modifying one of its elements.

Martyn

> exists("alist", 1, inherits=F)
[1] FALSE
> mydata <- list(alist = list(one=1,two=1))
> attach(mydata)
> alist
$one
[1] 1

$two
[1] 1

> alist$one <- 2
> alist[[2]] <- 3
> alist
$one
[1] 1

$two
[1] 1

> exists("alist", 1, inherits=F)
[1] FALSE
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