coef.hclust             package:cluster             R Documentation

Agglomerative Coefficient for 'hclust' Objects

Description:

     Computes the "agglomerative coefficient", measuring the clustering
     structure of the dataset.

     For each observation i, denote by m(i) its dissimilarity to the
     first cluster it is merged with, divided by the dissimilarity of
     the merger in the final step of the algorithm.  The agglomerative
     coefficient is the average of all 1 - m(i).  It can also be seen
     as the average width (or the percentage filled) of the banner
     plot.

     Because it grows with the number of observations, this measure
     should not be used to compare datasets of very different sizes.

Usage:

     coef.hclust(object, ...)
     ## S3 method for class 'hclust':
     coef(object, ...)
     ## S3 method for class 'twins':
     coef(object, ...)

Arguments:

  object: an object of class '"hclust"' or '"twins"', i.e., typically
          the result of 'hclust(.)','agnes(.)', or 'diana(.)'.

          Since 'coef.hclust' only uses 'object$heights', and
          'object$merge', 'object' can be any list-like object with
          appropriate 'merge' and 'heights' components. 

     ...: currently unused potential further arguments

Value:

     a number specifying the _agglomerative_ (or _divisive_ for 'diana'
     objects) coefficient as defined by Kaufman and Rousseeuw, see
     'agnes.object $ ac' or 'diana.object $ dc'.

Examples:

     data(agriculture)
     aa <- agnes(agriculture)
     coef(aa) # really just extracts aa$ac
     coef(as.hclust(aa))# recomputes

