1. Here is your example redone using proto: library(proto)
parent <- proto() child <- proto(a = 1) parent$child1 <- child child$parent.env <- parent # also just for illustration lets change a parent$child1$a # 1 child$a <- 2 parent$child1$a # 2 2. To redefine $<- use S3 or S4 but it can be done in conjunction with proto like this: # constructor node <- function(. = parent.frame(), ...) structure(proto(...), class = c("node", "proto")) "$<-.node" <- function(this, s, value) { if (s == ".super") parent.env(this) <- value if (is.function(value)) environment(value) <- this if (inherits(value, "node")) parent.env(value) <- this this[[as.character(substitute(s))]] <- value this } p <- node(a = 1) p$child <- node(b = 2) p$child$parent.env() p # same On 3/16/07, Yuk Lap Yip (Kevin) <[EMAIL PROTECTED]> wrote: > Hi Gabor, > > Thanks for the suggestions. I tried to look for the proto vignette > document but could not find it, could you tell me how to reach it? > > Besides, is it possible to define my own node object type with a > default behavior for the "<-" operator of its member variables being > referencing rather than copying? Any good reference material/ similar > code examples? > > Thanks. > > Gabor Grothendieck wrote: > > Lists are not good for this. There is an example in section 3.3 of > > the proto vignette of using proto objects for this. That section > > also references an S4 example although its pretty messy with S4. > > > > You might want to look at the graph, RBGL and graphviz packages > > in Bioconductor and the dynamicgraph, mathgraph and sna packages > > on CRAN. > > > > On 3/16/07, Yuk Lap Yip (Kevin) <[EMAIL PROTECTED]> wrote: > >> Hi all, > >> > >> I am rather new to R. Recently I have been trying to implement some > >> tree algorithms in R. I used lists to model tree nodes. I thought > >> something like this would work: > >> > >> parent <- list(); > >> child <- list(); > >> parent$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. > >> > > -- > > > 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.