MK wrote:
> Hi all,
>
> I'm very new to R and I'm trying to construct a threaded binary tree using
> recursive functions.
>
> I'm very confused was wondering if anyone had any R sample code they would
> share. I've come across a lot of C++ code(nothing in R) and this is not
> helping.
>
> best,
>
> MK
Not sure what you mean by a "threaded" binary tree, but I am enclosing
code below. It is from my forthcoming book on software development in
R.
Two caveats:
1. It hasn't been checked yet. There may be bugs, inefficiencies etc.
2. It does search and insert, not delete.
Norm Matloff
# routines to create trees and insert items into them are included
# below; a deletion routine is left to the reader as an exercise
# storage is in a matrix, say m, one row per node of the tree; a link i
# in the tree means the vector m[i,] = (u,v,w); u and v are the left and
# right links, and w is the stored value; null links have the value NA;
# the matrix is referred to as the list (m,nxt,inc), where m is the
# matrix, nxt is the next empty row to be used, and inc is the number of
# rows of expansion to be allocated when the matrix becomes full
# initializes a storage matrix, with initial stored value firstval
newtree <- function(firstval,inc) {
m <- matrix(rep(NA,inc*3),nrow=inc,ncol=3)
m[1,3] <- firstval
return(list(mat=m,nxt=2,inc=inc))
}
# inserts newval into nonempty tree whose head is index hdidx in the
# storage space treeloc; note that return value must be reassigned to
# tree; inc is as in newtree() above
ins <- function(hdidx,tree,newval,inc) {
tr <- tree
# check for room to add a new element
tr$nxt <- tr$nxt + 1
if (tr$nxt > nrow(tr$mat))
tr$mat <- rbind(tr$mat,matrix(rep(NA,inc*3),nrow=inc,ncol=3))
newidx <- tr$nxt # where we'll put the new tree node
tr$mat[newidx,3] <- newval
idx <- hdidx # marks our current place in the tree
node <- tr$mat[idx,]
nodeval <- node[3]
while (TRUE) {
# which direction to descend, left or right?
if (newval <= nodeval) dir <- 1 else dir <- 2
# descend
# null link?
if (is.na(node[dir])) {
tr$mat[idx,dir] <- newidx
break
} else {
idx <- node[dir]
node <- tr$mat[idx,]
nodeval <- node[3]
}
}
return(tr)
}
# print sorted tree via inorder traversal
printtree <- function(hdidx,tree) {
left <- tree$mat[hdidx,1]
if (!is.na(left)) printtree(left,tree)
print(tree$mat[hdidx,3])
right <- tree$mat[hdidx,2]
if (!is.na(right)) printtree(right,tree)
}
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