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In R I would like to make some graphs in which I use multicoloured lines as in the examples below. Perhaps I could do this using different lines placed next to each other, but the problem is that it is hard then to use the correct line width so that they are placed exactly next to each other without any white space in between (since the lwd argument of lines in the R graphics package is not in absolute coordinates). Is there perhaps any other way to specify that I would like to draw a single line with two or three (or more) different colours? (ideally corners and line cappings should look OK)

cheers, Tom

PS the application I am working on is to be able to draw phylogenies with polymorphic states as in the image below

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SlowLoris
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Tom Wenseleers
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    This question is a little vague. You should add a concrete example that illustrates exactly what you're trying to achieve (and what code you've written so far). My only thought at the moment is that you should be using `rect`'s not lines. – joran Jun 19 '13 at 20:14
  • I'd write an algorithm which creates either sets of rectangles or, preferably, polygons which match your desired path shapes. It's not as hard as you might think :-) – Carl Witthoft Jun 20 '13 at 11:29

1 Answers1

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From what I gather from the help of par, the lwd parameter differs from device to device. For x11 it states that "Line widths as controlled by par(lwd =) are in multiples of 1/96inch". Based on the defined lwd, I needed to convert this width to the x and y units of the graph in order to correctly offset the following lines.

So now I have your lines able to turn a corner - some adjustments to the lines are still needed in order to get them to all end at the same length (e.g. subtract the offset from the last value in the series).

Example:

x <- c(1:10, rep(1, 10))
y <- c(rep(1, 10), 1:10)
lwd <- 20

x11() #lwd is multiples of 1/96 inches (from help info)

plot(y ~ x, t="l", lend=2, ljoin=2, lwd=lwd, col=3, xlim=c(0,11), ylim=c(0,11))

x.units.per.inch <- (par("usr")[2] - par("usr")[1]) / par("pin")[1]
y.units.per.inch <- (par("usr")[4] - par("usr")[3]) / par("pin")[2]

x.offset <- x.units.per.inch * 1/96 * lwd
y.offset <- y.units.per.inch * 1/96 * lwd

lines(x + x.offset, y + y.offset, lend=2, ljoin=2, lwd=lwd, col=2)
lines(x - x.offset, y - y.offset, lend=2, ljoin=2, lwd=lwd, col=4)

enter image description here

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Marc in the box
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  • I think you need to demonstrate that your approach can "turn the corner" properly. – IRTFM Jun 19 '13 at 20:39
  • Many thx for this - that's going well in the right direction - only other problem I am stuck with though is how to deal with corners? (even if in my case I only have right corners) Would it be easier by any chance to work with rect's rather than lines? – Tom Wenseleers Jun 19 '13 at 20:43
  • @TomWenseleers - hope that helps now. I think using `rect` will also require an offset to get the effect that you want. It is indeed complicated... – Marc in the box Jun 19 '13 at 20:58
  • Many thanks for this - that should get me going - no worries! I was just looking at the shape package too, that has a function filledshape which allows one to specify a custom shape with custom fill colours with a custom number of steps and arbitrary rotation, presumably that might work as well... – Tom Wenseleers Jun 19 '13 at 21:12