Using grid.layout inside grid.layout with grid package: naming of the viewports affects plotting

Hi

The essence of your problem is that seekViewport() is much more 
ambiguous than downViewport().

Your set up involves creating a hierarchy of viewports four deep, with 
eight viewport paths (vpPaths) in total ...

vp1::A::vp2::plot1
            ::plot2
    ::B::vp3::plot1
            ::plot2
    ::C::vp4::plot1
            ::plot2
    ::D::vp5::plot1
            ::plot2

... and an important feature of that set of vpPaths is that the viewport 
name "plot1" (and "plot2") occurs more than once.

That is not necessarily a problem because you can distinguish between 
the different instances of "plot1" with complete paths, like this ...

downViewport("vp1::B::vp3::plot1")

... or by navigating part way down the tree of viewports first to a 
point where there is only one "plot1" viewport below it ...

downViewport("B")
downViewport("plot1")

However, seekViewport("plot1") does NOT do either of those things.  It 
does ...

upViewport(0) # go right up to the ROOT viewport
downViewport("plot1")

... and that will just find the first "plot1" match, which is the one 
below viewport "A".

The seekViewport() function should not therefore be relied on in 
non-interactive settings.  In fact, if you are writing code for general 
use, you should probably be much more disciplined about how you navigate 
between your viewports and make use of upViewport() and unambiguous 
downViewport() calls so that you know which viewport you will end up in. 
  The code below demonstrates a more disciplined version of your 
viewport set up ...

library(grid)
stackedplot <- function(main=""){
   top.vp <- viewport(
     layout=grid.layout(2, 1))
   p1 <- viewport(layout.pos.col=1, layout.pos.row=1, name="plot1")
   p2 <- viewport(layout.pos.col=1, layout.pos.row=2, name="plot2")
   splot <- vpTree(top.vp, vpList(p1,p2))
   pushViewport(splot)
   upViewport()
   downViewport("plot1")
   grid.rect(width=unit(0.9, "npc"), height=unit(0.9, "npc"))
   grid.text(paste(main, 1))
   upViewport()
   downViewport("plot2")
   grid.rect(width=unit(0.9, "npc"), height=unit(0.9, "npc"))
   grid.text(paste(main, 1))
   upViewport(2)
  }

grid.newpage()
multitop.vp <- viewport(layout=grid.layout(2,2))
pl1 <- viewport(layout.pos.col=1, layout.pos.row=1, name="A")
pl2 <- viewport(layout.pos.col=1, layout.pos.row=2, name="B")
pl3 <- viewport(layout.pos.col=2, layout.pos.row=1, name="C")
pl4 <- viewport(layout.pos.col=2, layout.pos.row=2, name="D")
vpall <- vpTree(multitop.vp, vpList(pl1,pl2,pl3,pl4))
pushViewport(vpall)
upViewport()
downViewport("A")
stackedplot(main="A")
upViewport()
downViewport("B")
stackedplot(main="B")
upViewport()
downViewport("C")
stackedplot(main="C")
upViewport()
downViewport("D")
stackedplot(main="D")
upViewport(2)

Hope that helps

Paul

R version 3.1.1 (2014-07-10)
Platform: i386-w64-mingw32/i386 (32-bit)

locale:
[1] C

attached base packages:
[1] grid      stats     graphics  grDevices utils     datasets  methods   base

loaded via a namespace (and not attached):
[1] tools_3.1.1


I have a plotting function to produce plots with stacked plots (for simplicity, here two rectangles).

library(grid)
stackedplot <- function(main=""){
   top.vp <- viewport(
     layout=grid.layout(2, 1))
   p1 <- viewport(layout.pos.col=1, layout.pos.row=1, name="plot1")
   p2 <- viewport(layout.pos.col=1, layout.pos.row=2, name="plot2")
   splot <- vpTree(top.vp, vpList(p1,p2))
   pushViewport(splot)
   seekViewport("plot1")
   grid.rect(width=unit(0.9, "npc"), height=unit(0.9, "npc"))
   seekViewport("plot2")
   grid.rect(width=unit(0.9, "npc"), height=unit(0.9, "npc"))
  }

For creating a 2x2 grid with four stacked plots I tried to use the following code:

grid.newpage()
multitop.vp <- viewport(layout=grid.layout(2,2))
pl1 <- viewport(layout.pos.col=1, layout.pos.row=1, name="A")
pl2 <- viewport(layout.pos.col=1, layout.pos.row=2, name="B")
pl3 <- viewport(layout.pos.col=2, layout.pos.row=1, name="C")
pl4 <- viewport(layout.pos.col=2, layout.pos.row=2, name="D")
vpall <- vpTree(multitop.vp, vpList(pl1,pl2,pl3,pl4))
pushViewport(vpall)
seekViewport("A")
stackedplot(main="A")
seekViewport("B")
stackedplot(main="B")
seekViewport("C")
stackedplot(main="C")
seekViewport("D")
stackedplot(main="D")

This does not work as all the plots are plotted in the same cell of the grid (viewport A). However, if I plot them in a reversed order, the plots arrange as was supposed to: D to D, C to C and so on.

seekViewport("D")
stackedplot(main="D")
seekViewport("C")
stackedplot(main="C")
seekViewport("B")
stackedplot(main="B")
seekViewport("A")
stackedplot(main="A")

I tried with different names and found out that if I plot in reversed alphabetical order everything works fine. Once I try to plot in a viewport with a name earlier in alphabetical order, all other plots thereafter are plotted in the same viewport.

Why is this happening?

Regards,
Satu Helske

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