New version of plotSimmap (& plotTree) for plotting leftward facing phylogenies

I was working on fixing some bugs in the phytools function phenogram when I suddenly realized how easy it would be to add left-direction plotted trees to the function plotSimmap. We do this with two simple switches. First, when we open a new plotting window we make the x-axis a "reverse axis" by reversing the vector xlim (i.e., such that xlim[1]>xlim[2]). This, without any further changes to the code, will flip all the branches of the tree to run right-to-left. Next, we change the position of the plotted text relative to the end of each leaf in the tree. In a rightward plotted tree, we want this text to be left-aligned and begin where each terminus ends running rightward. A leftward plotted tree needs right-aligned text pointing leftward. This can be changed using the text argument pos, i.e.:

pos<-if(direction=="leftwards") 2 else 4

where 2 and 4 indicate that text should be added to the left of or to the right of the plotting coordinate, respectively.

The updated code for plotSimmap is here. The following is a quick a demo of the new version in action:

> require(phytools)
> source("plotSimmap.R")
> Q<-matrix(c(-1,1,1,-1),2,2)
> tree<-sim.history(pbtree(n=40,scale=1),Q,nsim=2)
> cols<-c("blue","red"); names(cols)<-c(1,2)
> layout(matrix(c(1,2),1,2))
> plotSimmap(tree[[1]],cols,direction="rightwards",lwd=3, pts=F)
> plotSimmap(tree[[2]],cols,direction="leftwards",lwd=3, pts=F)

One known issue is that plotSimmap(...,direction="leftwards",node.numbers=T) doesn't work. This appears to be because the 'graphics' function symbols, which called internally to plot rectangles around each node number, doesn't seem to like a reversed x-axis. If I turn symbols off manually, i.e. just plotting text and no rectangles, the node numbers show up fine.

That's it for now.