[R] Listing all binary trees of an ordinal set

[David Winsemius]

On Jun 18, 2012, at 5:25 PM, elmo wrote:

> Hi all,
>
> I'm new to R, have been reading books and trying to get started  
> coding too.
> The first thing of substance I've been trying to do is to create a  
> function
> to return a list of all binary trees of a list of ordinals.  So, for
> example, an input of list(3,1,2,4) would return:

Please do not cross-post (but DO read the Posting Guide where this was  
is requested). You have already gotten an answer on StackOverflow.

-- 
David.
>
> list(list(1, list(2, list(3, 4))),
>       list(1, list(list(2, 3), 4)),
>       list(list(1, 2), list(3, 4)),
>       list(list(1, list(2, 3)), 4),
>       list(list(list(1, 2), 3), 4))
>
> I've been trying recursions but nothing I've written has been both  
> complete
> and correct in the final formatting, and I'm sort of clueless when  
> it comes
> to recursive wrappers.  For example, one function I wrote,
>
> g=function(x) {
>  len.x = length(x);
>  if (len.x > 2)
>  {
>    y=list()
>    for (i in 1:(len.x-1))
>       y[[i]] = list(g(x[1:i]),g(x[-i:-1]))
>    return(y)
>  }
>  else return(x)
> }
>
> trim = function(x) {
>  for (i in 1:length(x)) {
>    if ((length(x[[i]]) == 1) && is.list(x[[i]]))
>      x[[i]] = x[[i]][[1]]
>  }
>  return(x)
> }
>
> findBinTreesOrd=function(x) {
>  x.lst = sort(unlist(x))
>  all.bin.trees = g(x.lst)
>  trim(all.bin.trees)
> }
>
> returns the trees in a compact, recursively nested form that I  
> haven't found
> a way to expand to the format that I desire.  Any help in either  
> writing a
> wrapper for that or a different approach to achieve what I'm trying  
> to get
> would be greatly appreciated--again, I'm quite new to R and am still  
> shaky
> with the powers and constraints that come with it.
>
> LM
>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/Listing-all-binary-trees-of-an-ordinal-set-tp4633753.html
> Sent from the R help mailing list archive at Nabble.com.
>
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David Winsemius, MD
West Hartford, CT