[R] Creating grid graphics with grid.layout

[Paul Murrell]

Hi

If using integer indices is awkward, you could push a viewport tree with 
the relevant viewports given useful names.  Then you can downViewport() 
using the names (if those plots are lattice plots, then you might even 
be able to use the 'draw.in' argument).  Is that the sort of thing you 
are looking for?

Paul


Jeff Horner wrote:
> Hi,
> 
> I recently created a function which uses grid with a viewport 
> constructed with grid.layout() to position four plots on a plot device. 
> My question is what's the best way to programatically traverse each 
> element of the viewport?
> 
> The grid is 5x5 and the four plots occupy positions (2,2), (4,2), (2,4), 
> and (4,4).
> 
> Here's the viewport code:
> 
>   pushViewport(
>          viewport(
>              layout=grid.layout(
>                  nrow=5,
>                  ncol=5,
>                  widths=unit(
>                      c(margin[2],1,margin[6],1,margin[4]),
>                      c('npc','null','npc','null','npc')),
>                  heights=unit(
>                      c(margin[3],1,margin[5],1,margin[1]),
>                      c('npc','null','npc','null','npc'))
>              )
>          )
>      )
> 
> margin is a numeric vector of length 6 which resp defines the bottom, 
> left, top, right, horizontal, and veritical margins (the cross hairs 
> between the 4 plots). This is to allow the user to define how much 
> margin should exist around all plots and between the plots.
> 
> I then use lapply to visit only those viewports to place the plots by 
> specifying an x and y vector like so:
> 
> x <- c(2,4,2,4)
> y <- c(2,2,4,4)
> i <- 1
> lapply(list(plot1,plot2,plot3,plot4),function(j){
>     print(j,vp=viewport(layout.pos.col=x[i],layout.pos.row=y[i])
>     i <<- i + 1
> })
> 
> Looks kludgey. Is there a better way?
> 
> Also, I created debug code to visit those viewports where *nothing* is 
> supposed to be printed except for a grey box with black edges:
> 
> z <- outer(logical(5),logical(5),"==")
> for (i in 1:length(x)) z[x[i],y[i]] <- FALSE
> for (i in 1:5){
>     for (j in 1:5){
>        if (z[i,j])
>           grid.rect(gp=gpar(fill="grey"),
>             vp=viewport(layout.pos.col=i,layout.pos.row=j))
>     }
> }
> 
> This looks kludgey as well. Any other ways outer there that are more 
> elegant?
> 
> Thanks,
> 
> Jeff
> 
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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/