picksubset

 function [f,idx,fnot] = picksubset(m,num,seed)

 <m> is a matrix
 <num> is
   X indicating the size of the subset to pick out
   [X Y] where X is the total number of sets and Y is the set number to pull out.
     in this case, the sets are mutually exclusive and they collectively
     comprise the original <m> matrix.  note that the number of things in each
     set may be slightly different.
 <seed> (optional) is the rand state to use.
   default: 0.

 return:
  <f> as a vector with a random subset of <m>.
  <idx> as a vector of the indices of the elements that we picked.
  <fnot> as a vector with the remaining elements of <m>.

 note that if you try to pick out a subset bigger than <m>,
 we will just return as many elements as there are in <m>.

 example:
 picksubset(randn(10,10),10)

0001 function [f,idx,fnot] = picksubset(m,num,seed)
0002 
0003 % function [f,idx,fnot] = picksubset(m,num,seed)
0004 %
0005 % <m> is a matrix
0006 % <num> is
0007 %   X indicating the size of the subset to pick out
0008 %   [X Y] where X is the total number of sets and Y is the set number to pull out.
0009 %     in this case, the sets are mutually exclusive and they collectively
0010 %     comprise the original <m> matrix.  note that the number of things in each
0011 %     set may be slightly different.
0012 % <seed> (optional) is the rand state to use.
0013 %   default: 0.
0014 %
0015 % return:
0016 %  <f> as a vector with a random subset of <m>.
0017 %  <idx> as a vector of the indices of the elements that we picked.
0018 %  <fnot> as a vector with the remaining elements of <m>.
0019 %
0020 % note that if you try to pick out a subset bigger than <m>,
0021 % we will just return as many elements as there are in <m>.
0022 %
0023 % example:
0024 % picksubset(randn(10,10),10)
0025 
0026 % input
0027 if ~exist('seed','var') || isempty(seed)
0028   seed = 0;
0029 end
0030 
0031 % do it
0032   prev = rand('state');
0033   rand('state',seed);
0034 len = length(m(:));
0035 if isscalar(num)
0036   idx = subscript(randperm(len),1:min(num,len));
0037 else
0038   numsets = num(1);
0039   whichset = num(2);
0040   indices = zeros(numsets,ceil(len/numsets));
0041   indices(1:len) = randperm(len);
0042   idx = filterout(indices(whichset,:),0);
0043 end
0044 f = m(idx);
0045 fnot = m(setdiff(1:numel(m),idx));
0046   rand('state',prev);