Label Vertices of a Tree by Branch Membership

Given a linear network which is a tree (acyclic graph), this function assigns a label to each vertex, indicating its position in the tree.

spatial, math
treebranchlabels(L, root = 1)

Linear network (object of class "linnet"). The network must have no loops.


Root of the tree. An integer index identifying which point in vertices(L) is the root of the tree.


The network L should be a tree, that is, it must have no loops.

This function computes a character string label for each vertex of the network L. The vertex identified by root (that is, vertices(L)[root]) is taken as the root of the tree and is given the empty label "".

  • If there are several line segments which meet at the root vertex, each of these segments is the start of a new branch of the tree; the other endpoints of these segments are assigned the labels "a", "b", "c" and so on.

  • If only one segment issues from the root vertex, the other endpoint of this segment is assigned the empty label "".

A similar rule is then applied to each of the newly-labelled vertices. If the vertex labelled "a" is joined to two other unlabelled vertices, these will be labelled "aa" and "ab". The rule is applied recursively until all vertices have been labelled.

If L is not a tree, the algorithm will terminate, but the results will be nonsense.


A vector of character strings, with one entry for each point in vertices(L).

See Also

deletebranch, extractbranch, treeprune for manipulating a network using the branch labels.

linnet for creating a network.

  • treebranchlabels
  # make a simple tree
  m <- simplenet$m
  m[8,10] <- m[10,8] <- FALSE
  L <- linnet(vertices(simplenet), m)
  plot(L, main="")
  # compute branch labels 
  tb <- treebranchlabels(L, 1)
  tbc <- paste0("[", tb, "]")
  text(vertices(L), labels=tbc, cex=2)
# }
Documentation reproduced from package spatstat, version 1.56-1, License: GPL (>= 2)

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