

   CCoonnssttrruucctt aann xxyyVVeeccttoorr oobbjjeecctt

        xyVector(x, y)

   AArrgguummeennttss::

          x: a numeric vector

          y: a numeric vector of the same length as `x'

   DDeessccrriippttiioonn::

        Create an object to represent a set of x-y pairs.  The
        resulting object can be treated as a matrix or as a
        data frame or as a vector.  When treated as a vector it
        reduces to the `y' component only.

        The result of functions such as `predict.spline' is
        returned as an `xyVector' object so the x-values used
        to generate the y-positions are retained, say for pur-
        poses of generating plots.

   VVaalluuee::

        An object of class `xyVector' with components

          x: a numeric vector

          y: a numeric vector of the same length as `x'

   AAuutthhoorr((ss))::

        Douglas Bates and Bill Venables

   EExxaammpplleess::

        data( women )
        ispl <- interpSpline( weight ~ height, women )
        weights <- predict( ispl, seq( 55, 75, len = 51 ))
        class( weights )
        plot( weights )
        weights

