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

From: Paul Murrell <p.murrell_at_auckland.ac.nz>
Date: Tue 05 Apr 2005 - 13:22:31 EST

Hi

This gives me a good starting point.

Paul

> 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@xscale; xmax <- vps\$plot.vp@xscale
> ymin <- vps\$plot.vp@yscale; ymax <- vps\$plot.vp@yscale
>
> 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@xscale; xmax <- vps\$plot.vp@xscale
> ymin <- vps\$plot.vp@yscale; ymax <- vps\$plot.vp@yscale
>
> 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 )
>
>
>
>
> On Fri, 2005-04-01 at 14:40 +0200, Martin Maechler wrote:
>

```>>>>>>>"Paul" == Paul Murrell <p.murrell@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.
>>    >>
>>
>>
```

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

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