nn <- function ( p, y, q )

#*****************************************************************************80
#
## nn performs nearest neighbor interpolation.
#
#  Licensing:
#
#    Copyright 2016 James P. Howard, II
#
#    The computer code and data files on this web page are distributed under
#    https://opensource.org/licenses/BSD-2-Clause, the BSD-2-Clause license.
#
#  Modified:
#
#    27 February 2020
#
#  Author:
#
#    Original R code by James Howard;
#    Modifications by John Burkardt.
#
#  Reference:
#
#    James Howard,
#    Computational Methods for Numerical Analysis with R,
#    CRC Press, 2017,
#    ISBN13: 978-1-4987-2363-3.
#
{
  if ( ncol ( p ) != ncol ( q ) )
  {
    stop ( "p and q must have the same number of columns!" )
  }

  qprime <- t ( matrix ( rep ( q, nrow ( p ) ), ncol ( p ) ) )

  d <- sqrt ( rowSums ( ( p - qprime )^2 ) )

  return ( y[which.min(d)] )
}