[R] assign to an element of a vector

Brahm, David David.Brahm at geodecapital.com
Fri Apr 29 22:23:18 CEST 2005

Fernando Saldanha [fsaldan1 at gmail.com] wrote:
> I am trying to find a way to assign values to elements of a vector
> that will be defined by a user.
> > a <- c(1,2,3)
> > get('a')[1] <- 0
> Error: Target of assignment expands to non-language object

Try this function:
g.assign <- function(i, pos=1, ..., value) {
  x <- if (pos > 0) get(i, pos) else get(i, , parent.frame())
  x[...] <- value
  if (pos > 0) assign(i, x, pos) else assign(i, x, , parent.frame())

Your example becomes:
R> a <- c(1,2,3)
R> g.assign("a", pos=1, 1, value=0)

Note you use a positive <pos> (usually pos=1) for "global" variables,
pos=0 for "local" variables inside a function.  The <...> construction
this function to work for arrays too, but the downside is that you must
"value=" explicitly.

-- David Brahm (brahm at alum.mit.edu)

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