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cut.m

## Copyright (C) 1996, 1997  Kurt Hornik
## 
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2, or (at your option)
## any later version.
## 
## This program is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
## General Public License for more details. 
## 
## You should have received a copy of the GNU General Public License
## along with this file.  If not, write to the Free Software Foundation,
## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

## usage:  cut (X, BREAKS)
##
## Create categorical data out of numerical or continuous data by
## cutting into intervals.
##
## If BREAKS is a scalar, the data is cut into that many equal-width
## intervals. If BREAKS is a vector of break points, the category has
## length(BREAKS)-1 groups.
##
## Returns a vector of the same size as X telling which group each point
## in X belongs to.  Groups are labelled from 1 to the number of groups;
## points outside the range of BREAKS are labelled by NaN.

## Author:  KH <Kurt.Hornik@ci.tuwien.ac.at>
## Description:  Cut data into intervals

function group = cut (X, BREAKS)
  
  if (nargin != 2)
    usage ("cut (X, BREAKS)");
  endif

  if !is_vector (X)
    error ("cut:  X must be a vector");
  endif
  if is_scalar (BREAKS)
    BREAKS = linspace (min (X), max (X), BREAKS + 1);
    BREAKS(1) = BREAKS(1) - 1;
  elseif is_vector (BREAKS)
    BREAKS = sort (BREAKS);
  else
    error ("cut:  BREAKS must be a scalar or vector");
  endif

  group = NaN * ones (size (X));
  m = length (BREAKS);
  if any (k = find ((X >= min (BREAKS)) & (X <= max (BREAKS))))
    n = length (k);
    group(k) = sum ((ones (m, 1) * reshape (X(k), 1, n))
                > (reshape (BREAKS, m, 1) * ones (1, n)));
  endif

endfunction

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