Plotting terminal edges of the tree different colors depending (or not) on a discrete character using phytools

I recently received the following request:

“I would love to know if there is any way of extracting and colouring only a certain set of the terminal edges of the phylogeny, based on the tip labels. For example, using edge.color within plot.phylo based on a vector of tips. Do you know of any code that could be used to do this.”

This is pretty straightforward to do using phytools. Note that it can also be done using plot.phylo in the ape package, but I'm going to focus on the phytools way for obvious reasons.

I'll image that I'm painting the terminal edges leading to each tip with different colors based on the state of a discrete trait - but we could modify our technique for any arbitrary grouping of tips.

Here's the tree & data:

library(phytools)
tree

## 
## Phylogenetic tree with 26 tips and 25 internal nodes.
## 
## Tip labels:
##  A, B, C, D, E, F, ...
## 
## Rooted; includes branch lengths.

x

## A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 
## c a c a a c c a a a b c c a c b a a b c c b c a a b 
## Levels: a b c

Now, let's say we want to color the edges blue & red respectively if the corresponding edge is in state b or c, respectively, and leave it black if the tip is in state a.

## identify the tips in states b or c
b<-names(x)[x=="b"]
b

## [1] "K" "P" "S" "V" "Z"

c<-names(x)[x=="c"]
c

##  [1] "A" "C" "F" "G" "L" "M" "O" "T" "U" "W"

## paint the edges
tt<-paintBranches(tree,edge=sapply(b,match,tree$tip.label),
    state="b",anc.state="a")
tt<-paintBranches(tt,edge=sapply(c,match,tree$tip.label),
    state="c")

Now we can plot our tree:

tt

## 
## Phylogenetic tree with 26 tips and 25 internal nodes.
## 
## Tip labels:
##  A, B, C, D, E, F, ...
## 
## The tree includes a mapped, 3-state discrete character with states:
##  a, b, c
## 
## Rooted; includes branch lengths.

cols<-setNames(c("black","blue","red"),c("a","b","c"))
plot(tt,colors=cols,lwd=4,split.vertical=TRUE,ftype="i")

Let's check this against a plot generated using dotTree:

dotTree(tree,x,colors=cols)

That's about it.

Tree & data for this demo were simulated as follows:

tree<-pbtree(n=26,tip.label=LETTERS)
Q<-matrix(c(-2,1,1,1,-2,1,1,1,-2),3,3)
rownames(Q)<-colnames(Q)<-letters[1:3]
x<-as.factor(sim.history(tree,Q)$states)