## Saturday, April 20, 2013

### Extracting the set of most inclusive clades with Strahler number i

This is a response to the following question about Strahler numbers of trees:

I have an additional question, if I may: how could I go about extracting clades of a certain order as unique groups? .... I've been trying to extract the groups based solely on the assigned Strahler number for each node, but the lower ranking identical numbers mess with the extraction (i.e create unique clades that are just subsets of a bigger clade of the same order).

This is not too hard. Here is some code that should do this:

sn<-strahlerNumber(tree)
i<-3 # this is the order we want to extract
sn<-sn[sn==i]
# get descendant tip numbers for all clades
ll<-lapply(as.numeric(names(sn)),getDescendants,tree=tree)
# figure out which ones are most inclusive
ff<-function(x,y) !all(sapply(x,"%in%",y))
GG<-sapply(ll,function(x,y) sapply(y,ff,x=x),y=ll)
ii<-which(colSums(GG)==(ncol(GG)-1))
phy=tree)
class(trees)<-"multiPhylo"

OK - let's try it out:

> tree<-pbtree(n=30)
> sn<-strahlerNumber(tree,plot=TRUE)
Apply the code from above, then plot with Strahler numbers to verify:
> nplots<-2*ceiling(length(trees)/2)
> layout(matrix(1:nplots,ceiling(nplots/2),2,byrow=TRUE))
> sNN<-lapply(trees,strahlerNumber,plot=TRUE)

Cool.