small plot with no margins - border with line width (lwd) equal to 1 not visible

Question

I've been trying to make some very tiny line graphs using base plotting functions, but am coming unstuck when trying to add a thin border.

This is via RGui on Windows 7, saving a png from the plot window.

Here's my code:

dev.new(width=1.3,height=0.3)
par(mar=c(0,0,0,0))

set.seed(13)
x <- 1:10
y <- runif(10)

plot(x,y,type="n",xaxs="i",yaxs="i",ylim=c(0,1))
polygon( c(1,x,max(x),0), c(0,y,0,0), col="lightblue", border=NA)
lines(x,y,lwd=1)

Everything is fine until I try to add a box with a line width of 1, giving:

box(lwd=1)

Now I can solve this by increasing the line width to 2, but this seems a bit of a hack.

box(lwd=2)

Using rect like rect(1,0,10,1) doesn't seem to give me an appropriate solution either, with the bottom and right borders not being visible.

Answer 1

To answer my own question thanks to @baptiste's tip-off, this is a device dependent issue due to RGui. If the image is saved directly out to file using png everything works as intended. E.g.:

dev.new(width=1.3,height=0.3)
# repeat from here onwards only for png call below
par(mar=c(0,0,0,0))
set.seed(13)
x <- 1:10
y <- runif(10)
plot(x,y,type="n",xaxs="i",yaxs="i",ylim=c(0,1),bty="n")
polygon( c(1,x,max(x),0), c(0,y,0,0), col="lightblue", border=NA)
lines(x,y,lwd=1)
box(lwd=1)

Saving out to png from the "R Graphics" window gives my original stuffed up image:

Going directly to file using png like:

png("textbox_direct.png",width=116,height=27)
# take code block from above
dev.off()

...gives the correct result:

Answer 2

Have you considered giving mar a small non-zero value:

dev.new(width=0.3,height=0.3)
par(mar=c(0.01,0.01,0.01,0.01))

set.seed(13)
x <- 1:10
y <- runif(10)

plot(x,y,type="n",xaxs="i",yaxs="i",ylim=c(0,1))
polygon( c(1,x,max(x),0), c(0,y,0,0), col="lightblue", border=NA)
lines(x,y,lwd=1)

box(lwd=1)

I admit I haven't quite figured out what the end-game might be, but when I do an interactive "stretch" of that very small screen-object, it does result in an all-around border.

I do recognize that I am on a Mac and saving this to a pdf file and converting it to a png file for SO-inclusion may not be precisely reproducible on a Linux or Windows device.

Answer 3

Another solution base in grid and gridBase package. The idea is to replace the box by grid.rect.

1. Use gridBase to get the base viewport
2. Introduce some offset (viewport y ) to show the bottom line
3. Reduce the width of the viewport to show the right line.

Here my code:

library(gridBase)
sp <- baseViewports()
vp <- sp$plot
vp$width <- unit(0.999,'npc')
vp$y <- unit(0.001,'npc')
pushViewport(vp)
grid.rect(gp=gpar(fill=NA))
upViewport(1)

EDIT thanks to @baptiste, you can simply get the same result using only grid.rect:

library(grid)
grid.rect(width = unit(0.999,'npc'),
          y = unit(0.5001, "npc"),
          gp=gpar(fill=NA))