# R: General Tree Structures

dendrogram {stats} | R Documentation

## General Tree Structures

### Description

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.

The code is still in testing stage and the API may change in the future.

### Usage

    as.dendrogram(object, ...)
    ## S3 method for class 'hclust':
    as.dendrogram(object, hang = -1, ...)

    ## S3 method for class '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, ...)

    ## S3 method for class 'dendrogram':
    cut(x, h, ...)

    ## S3 method for class 'dendrogram':
    print(x, digits, ...)

    ## S3 method for class 'dendrogram':
    rev(x)

    ## S3 method for class 'dendrogram':
    str(object, max.level = NA, digits.d = 3,
        give.attr = FALSE, wid = getOption("width"),
        nest.lev = 0, indent.str = "", stem = "--", ...)

    is.leaf(object)

### Arguments

`object` | any R object that can be made into one of class `"dendrogram"`.
`x` | object of class `"dendrogram"`.
`hang` | numeric scalar indicating how the height of leaves should be computed from the heights of their parents; see `plot.hclust`.
`type` | type of plot.
`center` | logical; if `TRUE`, nodes are plotted centered with respect to the leaves in the branch. Otherwise (default), plot them in the middle of all direct child nodes.
`edge.root` | logical; if true, draw an edge to the root node.
`nodePar` | a `list` of plotting parameters to use for the nodes (see `points`) or `NULL` by default which does not draw symbols at the nodes. The list may contain components named `pch`, `cex`, `col`, and/or `bg` each of which can have length two for specifying separate attributes for inner nodes and leaves.
`edgePar` | a `list` of plotting parameters to use for the edge `segments` and labels (if there's an `edgetext`). The list may contain components named `col`, `lty` and `lwd` (for the segments), `p.col`, `p.lwd`, and `p.lty` (for the `polygon` around the text) and `t.col` for the text color. As with `nodePar`, each can have length two for differentiating leaves and inner nodes.
`leaflab` | a string specifying how leaves are labeled. The default `"perpendicular"` write text vertically (by default). `"textlike"` writes text horizontally (in a rectangle), and `"none"` suppresses leaf labels.
`dLeaf` | a number specifying the distance in user coordinates between the tip of a leaf and its label. If `NULL` as per default, 3/4 of a letter width or height is used.
`horiz` | logical indicating if the dendrogram should be drawn horizontally or not.
`frame.plot` | logical indicating if a box around the plot should be drawn, see `plot.default`.
`h` | height at which the tree is cut.
`..., xlab, ylab, xaxt, yaxt` | graphical parameters, or arguments for other methods.
`digits` | integer specifying the precision for printing, see `print.default`.
`max.level, digits.d, give.attr, wid, nest.lev, indent.str` | arguments to `str`, see `str.default()`. Note that `give.attr = FALSE` still shows `height` and `members` attributes for each node.
`stem` | a string used for `str()` specifying the stem to use for each dendrogram branch.

### Details

Warning: This documentation is preliminary.

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]]` 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.

`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.

Objects of class `"hclust"` can be converted to class `"dendrogram"` using method `as.dendrogram`.

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

`is.leaf(object)` is logical indicating if `object` is a leaf (the most simple dendrogram). `plotNode()` and `plotNodeLimit()` are helper functions.

### Warning

Some operations on dendrograms (including plotting) make use of recursion. For very deep trees It may be necessary to increase `options("expressions")`: if you do you are likely to need to set the C stack size larger than the OS default if possible (which it is not on Windows).

### Note

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

### See Also

`order.dendrogram` also on the `labels` method for dendrograms.

### Examples

    require(graphics); require(utils)

    hc <- hclust(dist(USArrests), "ave")
    (dend1 <- as.dendrogram(hc)) # "print()" method
    str(dend1)          # "str()" method
    str(dend1, max = 2) # only the first two sub-levels

    op <- par(mfrow= c(2,2), mar = c(5,2,1,4))
    plot(dend1)
    ## "triangle" type and show inner nodes:
    plot(dend1, nodePar=list(pch = c(1,NA), cex=0.8, lab.cex = 0.8),
          type = "t", center=TRUE)
    plot(dend1, edgePar=list(col = 1:2, lty = 2:3), dLeaf=1, edge.root = TRUE)
    plot(dend1, nodePar=list(pch = 2:1,cex=.4*2:1, col = 2:3), horiz=TRUE)

    dend2 <- cut(dend1, h=70)
    plot(dend2$upper)
    ## leafs are wrong horizontally:
    plot(dend2$upper, nodePar=list(pch = c(1,7), col = 2:1))
    ##  dend2$lower is *NOT* a dendrogram, but a list of .. :
    plot(dend2$lower[[3]], nodePar=list(col=4), horiz = TRUE, type = "tr")
    ## "inner" and "leaf" edges in different type & color :
    plot(dend2$lower[[2]], nodePar=list(col=1),# non empty list
         edgePar = list(lty=1:2, col=2:1), edge.root=TRUE)
    par(op)
    str(d3 <- dend2$lower[[2]][[2]][[1]])

    nP <- list(col=3:2, cex=c(2.0, 0.75), pch= 21:22, bg= c("light blue", "pink"),
               lab.cex = 0.75, lab.col = "tomato")
    plot(d3, nodePar= nP, edgePar = list(col="gray", lwd=2), horiz = TRUE)
    addE <- function(n) {
          if(!is.leaf(n)) {
            attr(n, "edgePar") <- list(p.col="plum")
            attr(n, "edgetext") <- paste(attr(n,"members"),"members")
          }
          n
    }
    d3e <- dendrapply(d3, addE)
    plot(d3e, nodePar= nP)
    plot(d3e, nodePar= nP, leaflab = "textlike")

[Package stats version 2.6.0 Index]