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% File src/library/grid/man/grid.DLapply.Rd
% Part of the R package, https://www.R-project.org
% Copyright 1995-2013 R Core Team
% Distributed under GPL 2 or later

\name{grid.DLapply}
\alias{grid.DLapply}
\title{ Modify the Grid Display List }
\description{
  Call a function on each element of the current display list.
}
\usage{
grid.DLapply(FUN, ...)
}
\arguments{
  \item{FUN}{A function;  the first argument to this function
    is passed each element of the display list. 
  }
  \item{\dots}{Further arguments to pass to \code{FUN} .}
}
\value{
  The side effect of these functions
  is usually to modify the grid display list.
}
\details{
  This function is insanely dangerous (for the grid display list).

  Two token efforts are made to try to avoid ending up with complete
  garbage on the display list:

  \enumerate{
    \item The display list is only replaced once all new elements have
    been generated (so an error during generation does not result in a
    half-finished display list).
    \item All new elements must be either \code{NULL} or inherit from
    the class of the element that they are replacing.
  }
}
\seealso{
  \link{Grid}.
}
\examples{
grid.newpage()
grid.rect(width=.4, height=.4, x=.25, y=.75, gp=gpar(fill="black"), name="r1")
grid.rect(width=.4, height=.4, x=.5, y=.5, gp=gpar(fill="grey"), name="r2")
grid.rect(width=.4, height=.4, x=.75, y=.25, gp=gpar(fill="white"), name="r3")
grid.DLapply(function(x) { if (is.grob(x)) x$gp <- gpar(); x })
grid.refresh()
}
\keyword{dplot}