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## -*- texinfo -*-
## @deftypefn  {} {} pareto (@var{y})
## @deftypefnx {} {} pareto (@var{y}, @var{x})
## @deftypefnx {} {} pareto (@var{hax}, @dots{})
## @deftypefnx {} {@var{h} =} pareto (@dots{})
## Draw a Pareto chart.
##
## A Pareto chart is a bar graph that arranges 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 magnitude from left to right along the x-axis.
##
## 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.  For quality improvement, the first few contributing causes
## (leftmost bars as presented on the diagram) 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.
##
## Typically only the magnitude data @var{y} is present in which case
## @var{x} is taken to be the range @code{1 : length (@var{y})}.  If @var{x}
## is given it may be a string array, a cell array of strings, or a numerical
## vector.
##
## If the first argument @var{hax} is an axes handle, then plot into this axes,
## rather than the current axes returned by @code{gca}.
##
## The optional return value @var{h} is a 2-element vector with a graphics
## handle for the created bar plot and a second handle for the created line
## plot.
##
## 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
## @seealso{bar, barh, hist, pie, plot}
## @end deftypefn

function h = pareto (varargin)

  [hax, varargin, nargin] = __plt_get_axis_arg__ ("pareto", varargin{:});

  if (nargin < 1 || nargin > 2)
    print_usage ();
  endif

  y = varargin{1}(:).';
  if (nargin == 2)
    x = varargin{2}(:).';
    if (! iscell (x))
      if (ischar (x))
        x = cellstr (x);
      else
        x = cellstr (num2str (x(:)));
      endif
    endif
  else
    x = cellstr (int2str ([1:numel(y)]'));
  endif

  [y, idx] = sort (y, "descend");
  x = x(idx);
  cdf = cumsum (y);
  maxcdf = cdf(end);
  cdf ./= maxcdf;
  idx95 = find (cdf < 0.95, 1, "last") + 1;

  if (isempty (hax))
    [ax, hbar, hline] = plotyy (1 : idx95, y(1:idx95),
                                1 : length (cdf), 100 * cdf,
                                @bar, @plot);
  else
    [ax, hbar, hline] = plotyy (hax, 1 : idx95, y(1:idx95),
                                     1 : length (cdf), 100 * cdf,
                                     @bar, @plot);
  endif

  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%"},
              "ycolor", get (ax(1), "ycolor"));
  set (hline, "color", get (ax(1), "colororder")(1,:));
  set (ax(1:2), "xtick", 1:idx95, "xticklabel", x(1:idx95));

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

endfunction


%!demo
%! clf;
%! colormap (jet (64));
%! Cheese = {"Cheddar", "Swiss", "Camembert", "Munster", "Stilton", "Blue"};
%! Sold = [105, 30, 70, 10, 15, 20];
%! pareto (Sold, Cheese);
%! title ("pareto() demo #1");

%!demo
%! clf;
%! ## 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);
%! title ("pareto() demo #2");