## Copyright (C) 2007 David Bateman
## Copyright (C) 2003 Alberto Terruzzi
##
## This file is part of Octave.
##
## Octave 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 3 of the License, or (at
## your option) any later version.
##
## Octave 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 Octave; see the file COPYING.  If not, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {} pareto (@var{x})
## @deftypefnx {Function File} {} pareto (@var{x}, @var{y})
## @deftypefnx {Function File} {} pareto (@var{h}, @dots{})
## @deftypefnx {Function File} {@var{h} =} pareto (@dots{})
## Draw a Pareto chart, also called ABC chart. A Pareto chart is a bar graph 
## used to arrange information in such a way that priorities for process 
## improvement can be established. It organizes and displays information 
## to show the relative importance of data. The chart is similar to the 
## histogram or bar chart, except that the bars are arranged in decreasing 
## order from left to right along the abscissa.
## 
## The fundamental idea (Pareto principle) behind the use of Pareto 
## diagrams is that the majority of an effect is due to a small subset of the
## causes, so for quality improvement the first few (as presented on the 
## diagram) contributing causes to a problem usually account for the majority 
## of the result. Thus, targeting these "major causes" for elimination 
## results in the most cost-effective improvement scheme.
##
## The data are passed as @var{x} and the abscissa as @var{y}. If @var{y} is
## absent, then the abscissa are assumed to be @code{1 : length (@var{x})}.
## @var{y} can be a string array, a cell array of strings or a numerical
## vector.
##
## An example of the use of @code{pareto} is
##
## @example
## @group
## Cheese = @{"Cheddar", "Swiss", "Camembert", "Munster", "Stilton", ...
##    "Blue"@};
## Sold = [105, 30, 70, 10, 15, 20];
## pareto(Sold, Cheese);
## @end group
## @end example
## @end deftypefn

function h = pareto (varargin)

  if (nargin != 1 && nargin != 2)
    print_usage ();
  endif

  x = varargin {1}(:).';
  if (nargin == 2)
    y = varargin {2}(:).';
    if (! iscell (y))
      if (ischar (y))
	y = cellstr (y);
      else
	y = cellfun (@(x) num2str (x), num2cell (y), "UniformOutput", false);
      endif
    endif
  else
    y = cellfun (@(x) int2str (x), num2cell (1 : numel(x)), 
		 "UniformOutput", false);
  endif

  [x, idx] = sort (x, "descend");
  y = y (idx);
  cdf = cumsum (x);
  maxcdf = max(cdf);
  cdf = cdf ./ maxcdf;
  cdf95 = cdf - 0.95;
  idx95 = find(sign(cdf95(1:end-1)) != sign(cdf95(2:end)))(1);

  [ax, hbar, hline] = plotyy (1 : idx95, x (1 : idx95), 
			      1 : length(cdf), 100 .* cdf, 
			      @bar, @plot);

  axis (ax(1), [1 - 0.6, idx95 + 0.6, 0, maxcdf]);
  axis (ax(2), [1 - 0.6, idx95 + 0.6, 0, 100]);
  set (ax(2), "ytick", [0, 20, 40, 60, 80, 100], 
       "yticklabel", {"0%", "20%", "40%", "60%", "80%", "100%"});
  set (ax(1), "xtick", 1 : idx95, "xticklabel", y (1: idx95));
  set (ax(2), "xtick", 1 : idx95, "xticklabel", y (1: idx95));

  if (nargout > 0)
    h = [hbar; hline];
  endif
  
endfunction

%!demo
%! close
%! Cheese = {"Cheddar", "Swiss", "Camembert", "Munster", "Stilton", "Blue"};
%! Sold = [105, 30, 70, 10, 15, 20];
%! pareto(Sold, Cheese);

%!demo
%! close
%! % Suppose that we want establish which products makes 80 % of turnover.
%! Codes = {"AB4","BD7","CF8","CC5","AD11","BB5","BB3","AD8","DF3","DE7"};
%! Value = [2.35 7.9 2.45 1.1 0.15 13.45 5.4 2.05 0.85  1.65]';
%! SoldUnits = [54723 41114 16939 1576091 168000 687197 120222 168195, ...
%!              1084118 55576]';
%! pareto (Value.*SoldUnits, Codes);
