%READDATAFILE Read one of the datafiles
%
% [B,NEXT,J] = READDATAFILE(A,N)
%
% INPUT
% A Datafile
% N Number of the file to be read
%
% OUTPUT
% B Dataset stored in file N
% NEXT Number of next file to be read, 0 if done
% J Indices of objects in A
%
% DESCRIPTION
% A datafile points to a dataset stored in a series of files. This
% routine reads one of them, but is designed to read them all in a loop.
% A typical example is shown below, computing the overall mean per class.
% If the preprocessing field of A is set, the listed preprocessing is
% applied before returning.
% If the mappings field of A is set, the listed mappings are applied
% to B before returning.
%
% As the objects in A may be randomly distributed over the files, a
% reordering is performed internally in this routine. Consequently,
% objects may be returned in a different order than stored in A.
%
% [m,k,c] = getsize(a);
% nobjects = classsizes(a);
% u = zeros(c,k);
% next = 1;
% while next > 0
% [b,next] = readdatafile(a,next)
% u = u + meancov(b) .* repmat(nobjects',1,k);
% if next <= 0, break; end
% end
% u = u ./ repmat(classsizes(a)',1,k);
%
% SEE ALSO (<a href="http://37steps.com/prtools">PRTools Guide</a>)
% PRDATASET, DATAFILE