R help - May 2005 - Problem going back to a viewport with gridBase

I am setting up base plots -- one in viewport A and and one in B.  This part
works fine.  But if I go back to A after having done B and add
horizontal lines it seems
to not use the correct coordinates.  How do I tell it to resume using A's
coordinates?  I am already using par(fig = gridFIG()) but it seems that
that's
not enough to reestablish them.  What happens is that when I go back to 
A it draws the horizontal lines as if its relative to B's coordinates
rather than
restablishing A's coordinates.  As a result the horizontal lines are
drawn near the
bottom of the graph instead of at the correct heights.  Try running the code
below to see what I mean.

I have also tried to use baseViewports with this but did not have any
success.

How do I modify this example so that the horizontal red lines come out
at the appropriate levels?    Note that this is just an example and in 
the future I will want to have multiple viewports each with a base plot and
add arbitrary additional line or point plots to them so the solution needs
to be sufficiently general that I can so generalize it.

Thanks.


library(gridBase)

opar <- par(no.readonly = TRUE)
grid.newpage()

# two columns, one row
unit. <- unit(c(1,1), c("null","null"))
pushViewport(viewport(layout = grid.layout(1, 2, widths = unit.)))

# draw green graph in first column (viewport A)
pushViewport(viewport(layout.pos.col = 1, name = "A"))
par(fig = gridFIG()); par(new = TRUE)
plot(1:10, col = "green", pch = 20)
upViewport(1)

# draw purple graph in second column (viewport B)
pushViewport(viewport(layout.pos.col = 2, name = "B"))
par(fig = gridFIG()); par(new = TRUE)
plot(1:100, col = "purple", pch = 18)
upViewport()

# go back to A and add horizontal grid lines
seekViewport("A")
par(fig = gridFIG())
abline(h=1:10, col = "red")  #### THESE DO NOT GET DRAWN AS EXPECTED
popViewport()

# go back to B and add vertical grid lines
seekViewport("B")
par(fig = gridFIG())
abline(v=1:10, col = "red")
popViewport()
par(opar)

Hi


Gabor Grothendieck wrote:
> I am setting up base plots -- one in viewport A and and one in B.  This
part
> works fine.  But if I go back to A after having done B and add
> horizontal lines it seems
> to not use the correct coordinates.  How do I tell it to resume using
A's
> coordinates?  I am already using par(fig = gridFIG()) but it seems that
that's
> not enough to reestablish them.  What happens is that when I go back to 
> A it draws the horizontal lines as if its relative to B's coordinates
> rather than
> restablishing A's coordinates.  As a result the horizontal lines are
> drawn near the
> bottom of the graph instead of at the correct heights.  Try running the
code
> below to see what I mean.
> 
> I have also tried to use baseViewports with this but did not have any
> success.
> 
> How do I modify this example so that the horizontal red lines come out
> at the appropriate levels?    Note that this is just an example and in 
> the future I will want to have multiple viewports each with a base plot and
> add arbitrary additional line or point plots to them so the solution needs
> to be sufficiently general that I can so generalize it.
> 
> Thanks.
> 
> 
> library(gridBase)
> 
> opar <- par(no.readonly = TRUE)
> grid.newpage()
> 
> # two columns, one row
> unit. <- unit(c(1,1), c("null","null"))
> pushViewport(viewport(layout = grid.layout(1, 2, widths = unit.)))
> 
> # draw green graph in first column (viewport A)
> pushViewport(viewport(layout.pos.col = 1, name = "A"))
> par(fig = gridFIG()); par(new = TRUE)
> plot(1:10, col = "green", pch = 20)
> upViewport(1)
> 
> # draw purple graph in second column (viewport B)
> pushViewport(viewport(layout.pos.col = 2, name = "B"))
> par(fig = gridFIG()); par(new = TRUE)
> plot(1:100, col = "purple", pch = 18)
> upViewport()
> 
> # go back to A and add horizontal grid lines
> seekViewport("A")
> par(fig = gridFIG())
> abline(h=1:10, col = "red")  #### THESE DO NOT GET DRAWN AS
EXPECTED
> popViewport()
> 
> # go back to B and add vertical grid lines
> seekViewport("B")
> par(fig = gridFIG())
> abline(v=1:10, col = "red")
> popViewport()
> par(opar)

The base, or "traditional", graphics system only records the *current*
plotting coordinates;  it does not retain a memory of previous plotting 
coordinates.  What your example does is *reposition* the plotting 
region, but to do what you want you would have to recreate the plotting 
coordinates of the first plot.  This is possible (at least in simple 
cases like the above), as shown below.  However, perhaps a better 
approach would be to use a combination of grid and lattice plots, where 
the coordinate systems are retained and don't need to be recreated.  An 
example of this approach is given at the end.

#######
# Modified example using gridBase
#######
library(gridBase)

opar <- par(no.readonly = TRUE)
grid.newpage()

# two columns, one row
unit. <- unit(c(1,1), c("null","null"))
pushViewport(viewport(layout = grid.layout(1, 2, widths = unit.)))

# draw green graph in first column (viewport A)
pushViewport(viewport(layout.pos.col = 1, name = "A"))
par(fig = gridFIG()); par(new = TRUE)
plot(1:10, col = "green", pch = 20)
upViewport(1)

# draw purple graph in second column (viewport B)
pushViewport(viewport(layout.pos.col = 2, name = "B"))
par(fig = gridFIG()); par(new = TRUE)
plot(1:100, col = "purple", pch = 18)
upViewport()

# go back to A and add horizontal grid lines
seekViewport("A")
par(fig = gridFIG()); par(new=TRUE)  #### extra par(new=TRUE)
plot(1:10, type="n", axes=FALSE, ann=FALSE)  #### RESET PLOT A AXES
abline(h=1:10, col = "red")
popViewport()

# go back to B and add vertical grid lines
seekViewport("B")
par(fig = gridFIG()); par(new=TRUE)  #### extra par(new=TRUE)
plot(1:100, type="n", axes=FALSE, ann=FALSE)  #### RESET PLOT B AXES
abline(v=1:10, col = "red")
popViewport()
par(opar)


#######
# Similar result but using grid and lattice
#######
library(grid)
library(lattice)

grid.newpage()

# two columns, one row
unit. <- unit(c(1,1), c("null","null"))
pushViewport(viewport(layout = grid.layout(1, 2, widths = unit.)))

# draw green graph in first column (viewport A)
pushViewport(viewport(layout.pos.col = 1, name = "A"))
# lattice plot instead of base plot
p1 <- xyplot(1:10 ~ 1:10, col="green", pch=20)
# prefix important so I can refer to it later
print(p1, newpage=FALSE, prefix="plotA")
upViewport(1)

# draw purple graph in second column (viewport B)
pushViewport(viewport(layout.pos.col = 2, name = "B"))
p2 <- xyplot(1:100 ~ 1:100, col="purple", pch=18)
print(p2, newpage=FALSE, prefix="plotB")
upViewport()

# go back to A and add horizontal grid lines
seekViewport(trellis.vpname("panel", 1, 1, prefix="plotA"))
# I'm working on a grid.abline() ...
grid.segments(x0=0, x1=1,
               y0=unit(1:10, "native"),
               y1=unit(1:10, "native"),
               gp=gpar(col="red"))

# go back to B and add vertical grid lines
seekViewport(trellis.vpname("panel", 1, 1, prefix="plotB"))
grid.segments(y0=0, y1=1,
               x0=unit(1:10, "native"),
               x1=unit(1:10, "native"),
               gp=gpar(col="red"))

upViewport(0)

Paul
-- 
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/

On 6/2/05, Paul Murrell <p.murrell@auckland.ac.nz>
wrote:
> Hi
Thanks.  I have mucked around in vpTree structures and discovered its
actually quite easy to specify children so I have changed my example
so that instead of naming the children of 'layout' and then remembering 
coordinates linked to the names of the children of 'layout' in 
the 'coords' structure (which really just duplicates state information
already available in grid) it simply follows the order
of the children of 'layout' directly.  This permits elimination of
'coords'
and the two naming functions.  Using the depth approach you advocate,
'with' also becomes shorter and I think I have it to the point where it
works
with both vpPath and viewport classes.  Once Deepayan implements 
the use.viewport= argument to print, 'with' can be eliminated too.  No 
questions this time but I thought I would post the latest version for
completeness. Regards.

[pushLayout is same as before except there are no names on the
children of 'layout' and the rest is new]

library(grid)
library(lattice)

pushLayout <- function(nr, nc, name="layout") {
  pushViewport(viewport(layout=grid.layout(nr, nc), name=name))
  for (i in 1:nr) {
    for (j in 1:nc) {
      pushViewport(viewport(layout.pos.row=i, layout.pos.col=j))
      upViewport()
    }
  }
  upViewport()
}

with.vpPath <- with.viewport <- function(data, expr, ...) {
      # if data is a vpPath it cannot be ROOT since NULL will never
dispatch here
      depth <- if (data$name == "ROOT") 0 else
downViewport(data$name)
      result <- eval.parent(substitute(expr))
      upViewport(depth)
      invisible(result)
}

grid.newpage()

# specify number of cells to fill and number of rows
n <- 5; nr <- 3

nc <- ceiling(n/nr)
downViewport(pushLayout(nr, nc))

vpt <- current.vpTree(all = FALSE)
for(k in 1:n) with(vpt$children[[k]],
      print( xyplot(v ~ v, list(v = 1:k)), newpage = FALSE )
)