dendrogram

General Tree Structures

Class "dendrogram" provides general functions for handling tree-like structures. It is intended as a replacement for similar functions in hierarchical clustering and classification/regression trees, such that all of these can use the same engine for plotting or cutting trees.

Usage

as.dendrogram(object, …)
# S3 method for hclust
as.dendrogram(object, hang = -1, check = TRUE, …)
# S3 method for dendrogram
as.hclust(x, …)
# S3 method for dendrogram
plot(x, type = c("rectangle", "triangle"),
      center = FALSE,
      edge.root = is.leaf(x) || !is.null(attr(x,"edgetext")),
      nodePar = NULL, edgePar = list(),
      leaflab = c("perpendicular", "textlike", "none"),
      dLeaf = NULL, xlab = "", ylab = "", xaxt = "n", yaxt = "s",
      horiz = FALSE, frame.plot = FALSE, xlim, ylim, …)
# S3 method for dendrogram
cut(x, h, …)
# S3 method for dendrogram
merge(x, y, …, height,
      adjust = c("auto", "add.max", "none"))
# S3 method for dendrogram
nobs(object, …)
# S3 method for dendrogram
print(x, digits, …)
# S3 method for dendrogram
rev(x)
# S3 method for dendrogram
str(object, max.level = NA, digits.d = 3,
    give.attr = FALSE, wid = getOption("width"),
    nest.lev = 0, indent.str = "",
    last.str = getOption("str.dendrogram.last"), stem = "--",
    …)
is.leaf(object)

Details

The dendrogram is directly represented as a nested list where each component corresponds to a branch of the tree. Hence, the first branch of tree z is z[[1]], the second branch of the corresponding subtree is z[[1]][[2]], or shorter z[[c(1,2)]], etc.. Each node of the tree carries some information needed for efficient plotting or cutting as attributes, of which only members, height and leaf for leaves are compulsory:

members

total number of leaves in the branch

height

numeric non-negative height at which the node is plotted.

midpoint

numeric horizontal distance of the node from the left border (the leftmost leaf) of the branch (unit 1 between all leaves). This is used for plot(*, center = FALSE).

label

character; the label of the node

x.member

for cut()$upper, the number of former members; more generally a substitute for the members component used for ‘horizontal’ (when horiz = FALSE, else ‘vertical’) alignment.

edgetext

character; the label for the edge leading to the node

nodePar

a named list (of length-1 components) specifying node-specific attributes for points plotting, see the nodePar argument above.

edgePar

a named list (of length-1 components) specifying attributes for segments plotting of the edge leading to the node, and drawing of the edgetext if available, see the edgePar argument above.

leaf

logical, if TRUE, the node is a leaf of the tree.

% This will often be a \code{\link{character}} which can % be used for plotting instead of the \code{text} attribute.}

cut.dendrogram() returns a list with components $upper and $lower, the first is a truncated version of the original tree, also of class dendrogram, the latter a list with the branches obtained from cutting the tree, each a dendrogram.

There are [[, print, and str methods for "dendrogram" objects where the first one (extraction) ensures that selecting sub-branches keeps the class, i.e., returns a dendrogram even if only a leaf. On the other hand, [ (single bracket) extraction returns the underlying list structure.

Objects of class "hclust" can be converted to class "dendrogram" using method as.dendrogram(), and since R 2.13.0, there is also a as.hclust() method as an inverse.

rev.dendrogram simply returns the dendrogram x with reversed nodes, see also reorder.dendrogram.

The merge(x, y, ...) method merges two or more dendrograms into a new one which has x and y (and optional further arguments) as branches. Note that before R 3.1.2, adjust = "none" was used implicitly, which is invalid when, e.g., the dendrograms are from as.dendrogram(hclust(..)).

nobs(object) returns the total number of leaves (the members attribute, see above).

is.leaf(object) returns logical indicating if object is a leaf (the most simple dendrogram).

plotNode() and plotNodeLimit() are helper functions.

Note

plot():

When using type = "triangle", center = TRUE often looks better.

str(d):

If you really want to see the internal structure, use str(unclass(d)) instead.

Warning

Some operations on dendrograms such as merge() make use of recursion. For deep trees it may be necessary to increase options("expressions"): if you do, you are likely to need to set the C stack size (Cstack_info()[["size"]]) larger than the default where possible.

See Also

dendrapply for applying a function to each node. order.dendrogram and reorder.dendrogram; further, the labels method.

Aliases

• dendrogram
• as.dendrogram
• as.dendrogram.dendrogram
• as.dendrogram.hclust
• as.hclust.dendrogram
• cut.dendrogram
• [[.dendrogram
• merge.dendrogram
• nobs.dendrogram
• plot.dendrogram
• print.dendrogram
• rev.dendrogram
• str.dendrogram
• is.leaf

Examples