[R] To convert an adjacency list model into a nested set model

From: Gesmann, Markus <Markus.Gesmann_at_lloyds.com>
Date: Tue 08 Mar 2005 - 22:29:49 EST

Dear R-help

I am wondering if somebody wrote some code to convert an adjacency list model into a nested set model.
In principal I want to do the same as John Celko mentioned it here with SQL:
http://groups.google.co.uk/groups?hl=en&lr=lang_en&selm=8j0n05%24n31%241 %40nnrp1.deja.com

Assume you have a tree structure like this

             /       \
           /           \
         Bert        Chuck 
                   /    |   \
                 /      |     \
               /        |       \
             /          |         \
        Donna        Eddie       Fred

in an adjacency list model:

> emp=c("Albert", "Bert", "Chuck", "Donna", "Eddie", "Fred")
> boss=c(NA, "Albert", "Albert", "Chuck", "Chuck", "Chuck")
> print(Personnel<-data.frame(emp, boss))

     emp boss
1 Albert <NA>
2 Bert Albert
3 Chuck Albert
4 Donna Chuck
5 Eddie Chuck
6 Fred Chuck

Then it is quite hard to find the all the supervisors of one employee. John's suggestion is to convert the adjacency list model into a nested set model.
The organizational chart would look like this as a directed graph:

            Albert (1,12)
            /        \
          /            \
    Bert (2,3)    Chuck (4,11)
                   /    |   \
                 /      |     \
               /        |       \
             /          |         \
        Donna (5,6)  Eddie (7,8)  Fred (9,10)

The data is than stored in the following form:

> lft=c(1,2,4,5,7,9)
> rgt=c(12,3,11,6,8,10)
> print(Per<-data.frame(emp, lft, rgt))
  emp lft rgt
1 Albert 1 12
2 Bert 2 3
3 Chuck 4 11
4 Donna 5 6
5 Eddie 7 8
6 Fred 9 10

To find now the supervisor of an employee all you have to do is to look where the employees lft figure is between lft and rgt. The supervisors of Eddie are therefore
> subset(Per, lft < 7 & rgt > 7)

     emp lft rgt
1 Albert 1 12
3 Chuck 4 11

In the site mentioned above John provides also some code to transform a adjacency list model into a nested set model. Does somebody know if there is already a package for this in R?

Kind Regards

Markus Gesmann

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