R devel - Apr 2008 - segments() with zero-length arguments (PR#11192)

Uwe Ligges suggested I post this on R-bugs as a wishlist item with a
proposed patch.  R considers zero-length arguments to segments() to be
an error.  I would like R to allow this and to return without an
error.  It occurs naturally in settings like

valid <- c(FALSE, FALSE, FALSE)
segments(x0[valid], y0[valid], x1[valid], y1[valid])

For what it may be worth, S-Plus does not consider zero-length
arguments to segments() be an error.


plot(1:10)
segments(1,1,10,10,col='green')
segments(numeric(0), numeric(0), numeric(0), numeric(0), col='green')
Error in segments(x0, y0, x1, y1, col = col, lty = lty, lwd = lwd, ...) : 
        invalid first argument


segments.proposal <-
  function (x0, y0, x1, y1, col = par("fg"), lty =
par("lty"),
            lwd = par("lwd"), ...) {
    if (length(x0)==0 && length(y0)==0 && length(x1)==0
&& length(y1)==0)
      return(invisible(NULL))
    .Internal(segments(x0, y0, x1, y1, col = col, lty = lty, lwd = lwd, ...))
}

segments.proposal(numeric(0), numeric(0), numeric(0), numeric(0),
col='green')

I think we should allow only all-zero arguments (at present any 
zero-length argument is an error), as per the R-level proposed code.

arrows() and rect() share the code so it is much cleaner to do this 
internally.

Done for R-devel.

On Thu, 17 Apr 2008, rmh at temple.edu wrote:
> Uwe Ligges suggested I post this on R-bugs as a wishlist item with a
> proposed patch.  R considers zero-length arguments to segments() to be
> an error.  I would like R to allow this and to return without an
> error.  It occurs naturally in settings like
>
> valid <- c(FALSE, FALSE, FALSE)
> segments(x0[valid], y0[valid], x1[valid], y1[valid])
>
> For what it may be worth, S-Plus does not consider zero-length
> arguments to segments() be an error.
>
>
> plot(1:10)
> segments(1,1,10,10,col='green')
> segments(numeric(0), numeric(0), numeric(0), numeric(0),
col='green')
> Error in segments(x0, y0, x1, y1, col = col, lty = lty, lwd = lwd, ...) :
>        invalid first argument
>
>
> segments.proposal <-
>  function (x0, y0, x1, y1, col = par("fg"), lty =
par("lty"),
>            lwd = par("lwd"), ...) {
>    if (length(x0)==0 && length(y0)==0 && length(x1)==0
&& length(y1)==0)
>      return(invisible(NULL))
>    .Internal(segments(x0, y0, x1, y1, col = col, lty = lty, lwd = lwd,
...))
> }
>
> segments.proposal(numeric(0), numeric(0), numeric(0), numeric(0),
col='green')
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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Oxford OX1 3TG, UK                Fax:  +44 1865 272595