Let me rephrase that. Lists do not support references but they could be used to represent trees.
list(a = list(a = 1, b = list(2, 3, d = list(4, 5)), c = list(4, 5)) is a tree whose top nodes are a, b, c and b contains three nodes 2, 3 and d and d contains 2 nodes. However, if you want to do it via references as requested then lists are not appropriate. On 3/16/07, Gabor Grothendieck <[EMAIL PROTECTED]> wrote: > Lists are not good for this. There is an example in section 3.3 of > the proto vignette of using proto objects for this. That section > also references an S4 example although its pretty messy with S4. > > You might want to look at the graph, RBGL and graphviz packages > in Bioconductor and the dynamicgraph, mathgraph and sna packages > on CRAN. > > On 3/16/07, Yuk Lap Yip (Kevin) <[EMAIL PROTECTED]> wrote: > > Hi all, > > > > I am rather new to R. Recently I have been trying to implement some > > tree algorithms in R. I used lists to model tree nodes. I thought > > something like this would work: > > > > parent <- list(); > > child <- list(); > > parent$child1 <- child; > > child$parent <- parent; > > > > When I tried to check whether a node is its parent's first child > > using "if (node$parent$child1 == node)", it always returned false. Then > > I realized that it does not really work because "parent$child1 <- child" > > actually makes a copy of child instead of referencing it. I think one > > possible fix is to keep a list of node objects, and make references > > using the positions in the list. For example, I think the following > > would work: > > > > parent <- list(); > > child <- list(); > > nodes <- list(parent, child); > > parent$child1 <- 2; > > child$parent <- 1; > > > > Then the "first child" test can be rewritten as "if > > (nodes[[nodes[[nodeId]]$parent]]$child1 == nodeId)". However, I would > > prefer not to implement trees in this way, as it requires the > > inconvenient and error-prone manipulations of node IDs. > > > > May I know if there is a way to make object references to lists? Or > > are there other ways to implement tree data structures in R? > > > > BTW, I checked how hclust was implemented, and noticed that it calls > > an external Fortran program. I would want a solution not involving any > > external programs. > > > > Thanks. > > > > -- > > > > > > God bless. > > > > Kevin > > > > ______________________________________________ > > R-help@stat.math.ethz.ch mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > > and provide commented, minimal, self-contained, reproducible code. > > > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.