Lattice's `panel.rug` produces different line length with wide plot

Question

When producing a wide plot in lattice with margins that include panel.rug(), the length of the lines in rugged margins is longer in the y-axis than x-axis:

library(lattice)
png(width=800, height=400)
xyplot(Fertility ~ Education, swiss, panel = function(x, y,...) {
  panel.xyplot(x, y, col=1, pch=16)
  panel.rug(x, y, col=1, end= ...)})
dev.off()

I would like those rug lines in x- and y-axes to be the same length regardless of the shape of a plot (note: right now the rug lines will only be the same length when the plot is square).

Maybe post this as two separate questions, one for lattice and one for ggplot2? — Josh O'Brien
Good point, will do, quite different graphical systems so it makes sense to separate it... — Geek On Acid
Yeah, especially since (given what's displayed on your nifty Tufte in R page), I'm guessing you want answers for both, rather than just for one or the other. — Josh O'Brien

Josh O'Brien Josh O'Brien · Accepted Answer · 2015-10-19T20:11:46

With lattice, just change the coordinate system used by panel.rug from its default ("npc") to "snpc":

library(lattice)

## png(width=800, height=400)
xyplot(Fertility ~ Education, swiss, panel = function(x, y,...) {
  panel.xyplot(x, y, col=1, pch=16)
  panel.rug(x = x, y = y,  
            x.units = rep("snpc", 2),  y.units = rep("snpc", 2), 
            col=1, end= ...)
})
## dev.off()

To see why this gets you what you want, refer to ?unit for its description of what those two coordinate systems mean:

 Possible ‘units’ (coordinate systems) are:

 ‘"npc"’ Normalised Parent Coordinates (the default).  The origin
      of the viewport is (0, 0) and the viewport has a width and
      height of 1 unit.  For example, (0.5, 0.5) is the centre of
      the viewport.

 ‘"snpc"’ Square Normalised Parent Coordinates.  Same as Normalised
      Parent Coordinates, except gives the same answer for
      horizontal and vertical locations/dimensions.  It uses the
      _lesser_ of npc-width and npc-height.  This is useful for
      making things which are a proportion of the viewport, but
      have to be square (or have a fixed aspect ratio).

Lattice's `panel.rug` produces different line length with wide plot

1 Answers