Bug fix in plotTree.singletons to permit multifurcating nodes

A phytools user correctly reports that the phytools function plotTree.singletons (which, as the function name suggests, plots trees containing singleton nodes) breaks if more than two edges emerge from a single node.

For instance:

library(phytools)
text<-"(A:0.1,(S:0.3)B:0.2,(C:0.3,D:0.4)E:0.5)F;"
tree<-read.tree(text=text)
tree ## doesn't work at all

## 
## Phylogenetic tree with 4 tips and 3 internal nodes.
## 
## Tip labels:
## [1] "A" "S" "B" "" 
## Node labels:
## [1] ""  "D" "C"
## 
## Rooted; includes branch lengths.

tree<-read.newick(text=text)
tree ## read in correctly

## 
## Phylogenetic tree with 4 tips and 3 internal nodes.
## 
## Tip labels:
## [1] "A" "S" "C" "D"
## Node labels:
## [1] "F" "B" "E"
## 
## Unrooted; includes branch lengths.

plotTree.singletons(tree)

## Error in xy.coords(x, y): 'x' and 'y' lengths differ

Ok, the user very helpfully identified a fix in the code to address this issue. I also seem to have found a simpler fix. The code is available here and will also be in the next version of phytools.

Let's plot with the fixed code:

source("map.to.singleton.R")
plotTree.singletons(tree)

OK, that's it.