R: Identify Clusters in a Dendrogram

identify.hclust {stats} | R Documentation

## Identify Clusters in a Dendrogram

### Description

`identify.hclust` reads the position of the graphics pointer when the (first) mouse button is pressed. It then cuts the tree at the vertical position of the pointer and highlights the cluster containing the horizontal position of the pointer. Optionally a function is applied to the index of data points contained in the cluster.

### Usage

    ## S3 method for class 'hclust'
    identify(x, FUN = NULL, N = 20, MAXCLUSTER = 20, DEV.FUN = NULL,
              ...)

### Arguments

`x` | an object of the type produced by `hclust`.
`FUN` | (optional) function to be applied to the index numbers of the data points in a cluster (see ‘Details’ below).
`N` | the maximum number of clusters to be identified.
`MAXCLUSTER` | the maximum number of clusters that can be produced by a cut (limits the effective vertical range of the pointer).
`DEV.FUN` | (optional) integer scalar. If specified, the corresponding graphics device is made active before `FUN` is applied.
`...` | further arguments to `FUN`.

### Details

By default clusters can be identified using the mouse and an `invisible` list of indices of the respective data points is returned.

If `FUN` is not `NULL`, then the index vector of data points is passed to this function as first argument, see the examples below. The active graphics device for `FUN` can be specified using `DEV.FUN`.

The identification process is terminated by pressing any mouse button other than the first, see also `identify`.

### Value

Either a list of data point index vectors or a list of return values of `FUN`.

### See Also

`hclust`, `rect.hclust`

### Examples

    ## Not run:
    require(graphics)

    hca <- hclust(dist(USArrests))
    plot(hca)
    (x <- identify(hca)) ##  Terminate with 2nd mouse button !!

    hci <- hclust(dist(iris[,1:4]))
    plot(hci)
    identify(hci, function(k) print(table(iris[k,5])))

    # open a new device (one for dendrogram, one for bars):
    dev.new() # << make that narrow (& small)
              # and *beside* 1st one
    nD <- dev.cur()            # to be for the barplot
    dev.set(dev.prev())  # old one for dendrogram
    plot(hci)
    ## select subtrees in dendrogram and "see" the species distribution:
    identify(hci, function(k) barplot(table(iris[k,5]), col = 2:4), DEV.FUN = nD)

    ## End(Not run)

[Package stats version 3.5.1 Index]