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

[Paul Murrell]

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.


gplot.hexbin() returns the viewports it used to produce the plot and the 
legend.  Here's an example of annotating the plot ...

  # capture the viewports returned
  vps <- plot( hexbin( x, y ), style = "nested.lattice")
  # push the viewport corresponding to the plot
  # this is actually a hexViewport rather than a plain grid viewport
  # so you use pushHexport rather than grid's pushViewport
  pushHexport(vps$plot.vp)
  # use "native" coordinates to draw relative to the axis scales
  grid.move.to(-2, -10, default.units="native")
  grid.line.to(2, 10, default.units="native",
               gp=gpar(col="yellow", lwd=3))
  # tidy up
  popViewport()

There's another annotation example at the bottom of the help page for 
gplot.hexbin

A grid.abline() function would obviously be a useful addition.  Must 
find where I put my todo list ...

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
> 
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-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/