On 6/1/05, Paul Murrell <p.murrell at auckland.ac.nz> wrote:
> Hi
>
>
> Gabor Grothendieck wrote:
> > [moved from r-help to r-devel]
> >
> > On 5/31/05, Paul Murrell <p.murrell at auckland.ac.nz> wrote:
> >
> >
> >>> # mm.row[j] gives the row in the layout of the jth cell
> >>> # mm.col[j] gives the col in the layout of the jth cell
> >>> mm <- matrix(seq(nr*nc), nr, nc)
> >>> mm.row <- c(row(mm))
> >>> mm.col <- c(col(mm))
> >>>
> >>> # go to next cell in the array
> >>> j <- j + 1 # increment position
> >>> pushViewport(viewport(layout.pos.row = mm.row[j], layout.pos.col = mm.col[j]))
> >>>
> >>>Is that how to do it or is there some layout/mfcol-like way?
> >>
> >>
> >>That is how to do it.
> >>
> >>As far as grid is concerned, all viewports are equal and grid has no
> >>idea whether a viewport corresponds to a "plot region" or a "margin" or
> >>whatever, so grid has no concept of which viewport is the "next" one to use.
> >>
> >
> >
> > OK. Thanks. One suggestion. Maybe the cells in a layout could have
> > an order to them and there could be an optional argument that takes a linear
> > index directly allowing easy linear traversals:
> >
> > for(i in seq(nr*nc)) {
> > pushViewport(viewport(i)) # might need different syntax here
> > xyplot(seq(i) ~ seq(i))
> > popViewport()
> > }
>
>
> I think this sort of thing can easily be built on top rather than into
> the existing system. For example, here's a function that pushes all of
> the basic cells in a layout using a simple naming convention:
>
> layoutVPname <- function(i, j) {
> paste("layoutViewport", i, ",", j, sep="")
> }
>
> layoutVPpath <- function(i, j, name="layout") {
> vpPath(name, layoutVPname(i, j))
> }
>
> 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,
> name=layoutVPname(i, j)))
> upViewport()
> }
> }
> upViewport()
> }
>
> And here's a use of the function to push lots of layout cells, then draw
> lattice plots in different cells using downViewport() to go to the cell
> with the appropriate name. In this case, we use cells by column, but
> simply reverse the order of the loops to use cells by row.
>
> pushLayout(2, 3)
> for (i in 1:2) {
> for (j in 1:3){
> depth <- downViewport(layoutVPpath(i, j))
> print(xyplot(seq(i*j) ~ seq(i*j)), newpage=FALSE)
> upViewport(depth)
> }
> }
>
>
> > and taking it one further perhaps 'with' could have a viewport method
> > that automatically pushes the viewport on entry and pops or moves
> > up one level on exit reducing the above to:
> >
> > for(i in seq(nr*nc)) with(viewport(i), xyplot(seq(i) ~ seq(i)))
>
>
> The raw grid functions have a 'vp' argument for this purpose. It would
> be nice if lattice functions had something similar (or maybe just
> print.trellis). Here's your example using the 'vp' argument to
> grid.text() (and using the layout that was pushed above) ...
>
> for (i in 1:2) {
> for (j in 1:3){
> grid.text(i*j, vp=layoutVPpath(i, j))
> }
> }
Thanks, again. I'll try modifying your example to fit my specific
application (which requires a linear column-wise traversal ending
at the nth cell where n may be less than the number of cells in the
matrix).