[R] hexbin and grid - input data values as coordinates

[Adaikalavan Ramasamy]

Thank you to Paul Murrell and Martin Maechler for their help.
pushHexport() and the rest of the codes have done the trick.

I spent the afternoon trying to code up something that might be used as
grid.abline() and grid.grid() before I read Martin's suggestion. Sigh. 

But here it is anyway in case you can salvage something out of my
inelegant solution.


mygrid.abline <- function(a=NULL, b=NULL, h=NULL, v=NULL,
                          vps, gp=gpar(col=1, lwd=1) ) {

  # a, b, h and v are as documented in help(abline)
  # vps and gp are the viewport and its graph parameters

  if(!is.null(h)){ a <- h; b <- 0 }
  if(!is.null(v)){ a <- v; b <- Inf }  
   
  pushHexport(vps$plot.vp)
  
  xmin <- vps$plot.vp at xscale[1];  xmax <- vps$plot.vp at xscale[2]
  ymin <- vps$plot.vp at yscale[1];  ymax <- vps$plot.vp at yscale[2]
  
  x0 <- max( (ymin - a)/b, xmin )
  x0 <- min( x0, xmax )
  y0 <- a + b*x0
  
  x1 <- min( (ymax - a)/b, xmax )
  x1 <- max( x1, xmin )
  y1 <- a + b*x1

  if( !is.finite(b) ){   # fudge for vertical lines
    x0 <- a;    x1 <- a
    y0 <- ymin; y1 <- ymax
  } 
  
  grid.move.to( x0, y0, default.units="native" )
  grid.line.to( x1, y1, default.units="native", gp=gp )

  popViewport()
  invisible( c( x0=x0, y0=y0, x1=x1, y1=y1 ) )
}


mygrid.grid <- function(vps, nx=NULL, ny=nx, 
                        gp=gpar(col=8, lwd=1, lty=2)){

  xmin <- vps$plot.vp at xscale[1];  xmax <- vps$plot.vp at xscale[2]
  ymin <- vps$plot.vp at yscale[1];  ymax <- vps$plot.vp at yscale[2]

  if( is.null(nx) ){ # the default

    vv <- seq(as.integer(xmin), as.integer(xmax), by=1)
    hh <- seq(as.integer(ymin), as.integer(ymax), by=1)

  } else {
  
    vv <- seq( xmin, xmax, length.out = nx + 1 )
    hh <- seq( ymin, ymax, length.out = ny + 1 )

  }

  sapply( vv, function(v) mygrid.abline( v=v, vps=vps, gp=gp ) )
  sapply( hh, function(h) mygrid.abline( h=h, vps=vps, gp=gp ) )
  invisible()
}


# USAGE EXAMPLE
x <- rnorm(1000)
y <- 10 + 1.6*x + rnorm(1000) 

vps <- plot( hexbin( x, y ), style = "nested.lattice")
mygrid.abline( a=10, b=2, vps=vps,  gp=gpar(col=2, lwd=3) )
mygrid.abline( a=10, b=-2, vps=vps, gp=gpar(col=1, lty=2) )
mygrid.grid( vps )


Regards, Adai


On Fri, 2005-04-01 at 14:40 +0200, Martin Maechler wrote:
> >>>>> "Paul" == Paul Murrell <p.murrell at auckland.ac.nz>
> >>>>>     on Fri, 01 Apr 2005 10:45:16 +1200 writes:
> 
>     Paul> Hi Adaikalavan Ramasamy wrote:
>     >> Dear all,
>     >> 
>     >> I am trying to use hexbin and read the very interesting
>     >> article on grid (
>     >> http://www.ci.tuwien.ac.at/Conferences/useR-2004/Keynotes/Murrell.pdf
>     >> ) and am hoping for some advice from more experienced
>     >> users of hexbin.
>     >> 
>     >> I am trying to visualise a data and fit a straight line
>     >> trough it. For example, here is how I would do it in the
>     >> usual way
>     >> 
>     >> # simulate data x <- rnorm(1000) y <- 5*x + rnorm(1000,
>     >> sd=0.5)
>     >> 
>     >> plot( x, y, pch="*" ) abline(0, 1, col=2)
>     >> 
>     >> 
>     >> And here is my failed attempt at fitting the "abline" on
>     >> hexbin
>     >> 
>     >> library(hexbin); library(grid) plot( hexbin( x, y ),
>     >> style = "nested.lattice") grid.move.to(0.2,0.2)
>     >> grid.line.to(0.8,0.8)
>     >> 
>     >> I realise that grid.* is taking plotting coordinates on
>     >> the graph but how do I tell it to use the coordinates
>     >> based on the data values ? For my real data, I would like
>     >> lines with different slopes and intercepts.
> 
> 
>     Paul> gplot.hexbin() returns the viewports it used to
>     Paul> produce the plot and the legend.  Here's an example of
>     Paul> annotating the plot ...
> 
>     Paul>   # capture the viewports returned vps <- plot(
>     Paul> hexbin( x, y ), style = "nested.lattice") # push the
>     Paul> viewport corresponding to the plot # this is actually
>     Paul> a hexViewport rather than a plain grid viewport # so
>     Paul> you use pushHexport rather than grid's pushViewport
>     Paul> pushHexport(vps$plot.vp) # use "native" coordinates to
>     Paul> draw relative to the axis scales grid.move.to(-2, -10,
>     Paul> default.units="native") grid.line.to(2, 10,
>     Paul> default.units="native", gp=gpar(col="yellow", lwd=3))
>     Paul> # tidy up popViewport()
> 
>     Paul> There's another annotation example at the bottom of
>     Paul> the help page for gplot.hexbin
> 
>     Paul> A grid.abline() function would obviously be a useful
>     Paul> addition.  Must find where I put my todo list ...
> 
> well, it seems to me that if you start with panel.abline() from
> lattice, you're almost finished right from start.
> 
> But then, sometimes the distance between "almost" and
> "completely" can become quite large...
> 
> Further, from the looks of it, if you finish it, panel.abline()
> could become a simple wrapper around grid.abline().
> 
> 
> Martin
> 
> 
>     Paul> Paul
> 
>     >> I am using the hexbin version 1.2-0 ( which is the devel
>     >> version ), R-2.0.1 and Fedora Core 3.
>     >> 
>     >> Many thanks in advance.
>     >> 
>     >> Regards, Adai
> 
>