[R] Age of an object?

[Martin Maechler]

>>>>> "Roger" == Roger Bivand <Roger.Bivand at nhh.no>
>>>>>     on Wed, 14 Dec 2005 15:14:47 +0100 (CET) writes:

    Roger> On Wed, 14 Dec 2005, Martin Maechler wrote:
    >> >>>>> "Kjetil" == Kjetil Brinchmann Halvorsen <kjetilbrinchmannhalvorsen at gmail.com>
    >> >>>>>     on Wed, 14 Dec 2005 08:59:24 -0400 writes:
    >> 
    Kjetil> Philippe Grosjean wrote:
    >> >> Martin Maechler wrote:
    >> >>>>>>>> "Trevor" == Trevor Hastie <hastie at stanford.edu>
    >> >>>>>>>> on Tue, 13 Dec 2005 12:51:34 -0800 writes:
    >> >>> 
    Trevor> It would be nice to have a date stamp on an object.  
    >> 
    Kjetil> Following up on my post of a few minutes ago, I tried to write an
    Kjetil> timestamp function
    >> 
    Kjetil> timestamp <- function(obj, moretext){
    Kjetil> comment(obj) <<- paste(Sys.time(), moretext, sep="\n")
    Kjetil> }
    >> 
    Kjetil> but this does'nt work.
    >> 
    >> >> myobj <- 1:10
    >> >> timestamp(myobj, "test")
    Kjetil> Error in timestamp(myobj, "test") : object "obj" not found
    >> >> 
    >> 
    >> Instead, I'd **strongly** recommend to define *two* functions,
    >> one "constructor" and one "inspector" :
    >> 
    >> "timestamp<-" <- function(obj, value) {
    >>    stamp <- paste(Sys.time(), value)
    >>    ## attr(obj,"timestamp") <- stamp
    >>    comment(obj) <- stamp
    >>    obj
    >> }

    Roger> This does treat any existing comment rather brutally, could stamp rather 
    Roger> be:

    Roger> stamp <- paste(Sys.time(), comment(obj), value)

    Roger> probably enhanced with some field separators to let the inspector grab 
    Roger> just its chunk? Something like DCF?

Sure (and hence Duncan TL's answer).
My main point was to define a "timestamp<-" function and
use 
    timestamp(......) <- ....

[instead of using functions that silently modify their arguments..]

Martin