dd_crossval.m

数据挖掘的工具箱,最新版的,希望对做这方面研究的人有用

function [y,z,I,Itr] = dd_crossval(x,I)
%DD_CROSSVAL
%
%   [Y,Z,I] = DD_CROSSVAL(X,I/NRBAGS)
% 
% Create cross-validation sets. When called for the first time:
%   [Y,Z,I] = DD_CROSSVAL(X,NRBAGS)
% Here I gives the number of bags and the permutated object indices.
% Y and Z give the new training set (containing (NRBAGS-1) pieces) and
% the new testing set (containing just 1 bag). All bags are of equal
% size, and class sizes are not taken into account. After gettting Y
% and Z the index variable I is updated. This is needed for the next
% call to dd_crossval.
%
% A typical run looks therefore something like:
% I = 5;
% for i=1:5
%   [Y,Z,I] = DD_CROSSVAL(X,I)
%   % do something useful wil Y and Z...
% end
%
% Note that you have to update the I each time, else you will get the
% same training and test set.
%
% See also: dd_error, dd_auc


% Copyright: D.M.J. Tax, [e-mail]
% Faculty of Applied Physics, Delft University of Technology
% P.O. Box 5046, 2600 GA Delft, The Netherlands

% Dxd, 4-7-99
% Dxd, 11-07-2002 renewed
% Dxd, 9-05-2003 for the new prtools

if (nargin<2)
	error('I or nrbags should be given!');
end
if length(I)==1
	nrbags = I; I = [];
end

% Check if the coding vector I is already defined
if ~isempty(I) % is already defined, go for the next bag.
	if (I(5)~=170673)
		error('Sorry, I has not the right format');
  end
  I(2) = I(2) + 1; % goto next bag
  if (I(2)>I(1))
	  warning('Maximal number of bags is extracted');
  end
else % Create a vector I to code for the bags
	nrx = size(x,1);
	I = [zeros(5,1); (mod(0:nrx-1,nrbags)+1)'];
	I(5) = 170673;
	I(1) = nrbags;
	I(2) = 1;      % number of active bag
end

% Extract the correct data given the I:
J = I(6:end);
Itr = find(J~=I(2));
y = x(Itr,:);
z = x((J==I(2)),:);

% One security check:
if nargout<3
	warning('You probably want to use the I for the next time!');
end

% Useful for inspection purposes:
if isdataset(y)
	y = setname(y,[getname(y),' (Xval train)']);
	z = setname(z,[getname(z),' (Xval test)']);
end

return