Allocating equal plot space to all of multiple plots with shared axes

Question

I'm trying to tile plots, specifically in a 2x3 matrix, for example:

x <- seq(1, 10, by=.01)
y <- 1/x

prms<-
  list(xlab=rep(c("", "x"), each=3),
       ylab=rep(c("y", "", ""), 2),
       xaxt=rep(c("n", "s"), each=3),
       yaxt=rep(c("s", "n", "n"), 2),
       mar=list(c(0  , 4.1, 4.1,   0),
                c(0  ,   0, 4.1,   0),
                c(0  ,   0, 4.1, 1.1),
                c(5.1, 4.1,   0,   0),
                c(5.1,   0,   0,   0),
                c(5.1,   0,   0, 1.1)))

par(mfrow=c(2, 3))
for (ii in 1:6){
  par(mar=prms$mar[[ii]])
  plot(x, y, type="l", lwd=2,
       xlab=prms$xlab[ii], ylab=prms$lab[ii],
       xaxt=prms$xaxt[ii], yaxt=prms$yaxt[ii])
}

Which produces:

I've suppressed the "inner" margins and axes because all x (resp., y) units are the same, so such axes would be redundant. However, as you can see, by squeezing the margins on the left- and rightmost plots, I've accidentally given the middle plots too much space (it's not as apparent, but the same trouble plagues the top vis-a-vis the bottom row).

Therein lies the conundrum. mfrow assigns equal space to each subplot (i.e., axes, margins, etc), not to each plot area. How can I change my approach so that each plotting area is of equal size, ceteris paribus (i.e., axes, etc. unchanged)? I thought of using layout, but couldn't think of a nice programmatic way to go about making sure everything has equal representation.

Answer 1

You may set mar to 0, and use oma to give the size of the outer margins. Axes are added to relevant plots in a loop. Common x and y axis labels are added with mtext and outer = TRUE

par(mfrow = c(2, 3),
    mar = c(0, 0, 0, 0),
    oma = c(4, 4, 0.5, 0.5))

for (i in 1:6) {
  plot(x, y, type = "l", axes = FALSE)
  if (i %in% c(4, 5, 6))
    axis(side = 1)
  if (i %in% c(1, 4))
    axis(side = 2)
  box()
  }

mtext("x values", side = 1, outer = TRUE, line = 2.5)
mtext("y values", side = 2, outer = TRUE, line = 2.5)

See also How to create multiple plots, each with same plot area size, when only one plot has axis labels?