Bug fix in drop.tip.densityMap

A phytools user reported the following peculiar bug with the phytools function drop.tip.densityMap:

## simulate some data
library(phytools)
tree<-pbtree(n=26,tip.label=LETTERS,scale=1)
Q<-matrix(c(-1,1,1,-1),2,2,dimnames=list(letters[1:2],letters[1:2]))
x<-as.factor(sim.history(tree,Q)$states)

## Done simulation(s).

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 
## b b b a a b a b b b b b a a a a b a a b b b a a a b 
## Levels: a b

## now replicate the error
trees<-make.simmap(tree,x,nsim=100)

## make.simmap is sampling character histories conditioned on the transition matrix
## Q =

##           a         b
## a -3.440867  3.440867
## b  3.440867 -3.440867

## (estimated using likelihood);
## and (mean) root node prior probabilities
## pi =

##   a   b 
## 0.5 0.5

## Done.

obj<-densityMap(trees,plot=FALSE)

## sorry - this might take a while; please be patient

plot(obj,lwd=4,outline=TRUE)

tips<-sample(tree$tip.label,5)
tips

## [1] "I" "U" "N" "G" "V"

obj<-drop.tip.densityMap(obj,tips)

## x should be an object of class "contMap"

I'm not sure when I introduced this bug, but it is now fixed and this will be in the next version of phytools (or if you update phytools from GitHub).

obj<-densityMap(trees,plot=FALSE)

## sorry - this might take a while; please be patient

source("../phytools/R/densityMap.R")
obj<-drop.tip.densityMap(obj,tips)
plot(obj,lwd=4,outline=TRUE)

That's it.