I have data such as:

in  out
1   3
2   3

This represents the following tree structure:

    1     2
      \ /
       3

Every tree will consist of sub-trees like this one, with 2 sources (in) and one destination (out). A slightly more complex tree is:

in  out
1   3
2   3
3   5
4   5

which represents this tree:

    1    2
      \ /
       3    4
        \ /
         5

So, the top of every tree will contain exactly 2 nodes, while the bottom will contain exactly 1 node and each level in between will contain exactly 2 nodes. There could be many levels. One final example:

in  out
1   3
2   3
3   5
4   5
5   7
6   7

which represents this tree:

    1    2                     level 1
      \ /
       3    4                  level 2
        \ /
         5    6                level 3
          \ /
           7                   level 4

How can I plot these trees in a nice way ? I can't use ggtree because the version of R that I have to use does not support it. I have looked at igraph and graph.tree but so far can't figure out how to do this.

If it matters, I would be happy plotting it upside down compared to how I have shown the trees above - or left to right.

CodePudding user response：

The input is an edge list so we can convert that to an igraph object and then plot it using the indicated layout. lay is a two column matrix givin gthe coordinates of the vertices and the matrix multiplication involving lay negates its second column thereby flipping it.

library(igraph)

DF <- data.frame(in. = 1:6, out. = c(3, 3, 5, 5, 7, 7)) # input

g <- graph_from_edgelist(as.matrix(DF[2:1]))
lay <- layout_as_tree(g)
plot(as.undirected(g), layout = lay %*% diag(c(1, -1)))