xyTable              package:grDevices              R Documentation

Multiplicities of (x,y) Points, e.g., for a Sunflower Plot

Description:

     Given (x,y) points, determine their multiplicity - checking for
     equality only up to some (crude kind of) noise.  Note that this is
     special kind of 2D binning.

Usage:

     xyTable(x, y = NULL, digits)

Arguments:

     x,y: numeric vectors of the same length; alternatively other (x,y)
          argument combinations as allowed by 'xy.coords(x,y)'.

  digits: integer specifying the significant digits to be used for
          determining equality of coordinates.  These are compared
          after rounding them via 'signif(*,digits)'.

Value:

     A list with three components of same length, 

       x: x coordinates, rounded and sorted.

       y: y coordinates, rounded (and sorted within 'x').

  number: multiplicities (positive integers); i.e., 'number[i]' is the
          multiplicity of '(x[i],y[i])'.

See Also:

     'sunflowerplot' which typically uses 'xyTable()'; 'signif'.

Examples:

     xyTable(iris[,3:4], digits = 6)

     ## Discretized uncorrelated Gaussian:

     require(stats)
     xy <- data.frame(x = round(sort(rnorm(100))), y = rnorm(100))
     xyTable(xy, digits = 1)

