Generate unique permutations (Matlab)

uniqueperms.m

function P = uniqueperms(varargin)

% This function allows two possible calling formats:
% perms_nodupes(syms)
% perms_nodupes(syms,counts)
%
% Here perms_nodupes returns all permutations of the vector SYMS.
% COUNTS is an optional vector indicating how many times each symbol should
% be included.  The following are equivalent:
%
% perms_nodupes([0 0 1 2])
% perms_nodupes([0 1 2], [2 1 1]);

if nargin==1
  syms = unique(varargin{1});
  counts = arrayfun(@(x) numel(find(varargin{1}==x)), syms);  
elseif nargin==2
  syms = varargin{1};
  counts = varargin{2};
else
  error('invalid arguments');
end

% Remove symbols that have count==0
ii = (counts==0);
syms(ii) = [];
counts(ii) = [];

% Check whether we have only one symbol left
if sum(counts)<=1
  P = syms;
  return
end

N = length(syms);
P = zeros(0, N);

for ii=1:N
  % start a permutation with syms[ii]
  s = syms(ii);
  q = uniqueperms(syms, counts - ((1:N)==ii));
  
  % stick the current symbol on the front of all the returned results:
  q = [repmat(s, size(q,1), 1) q];
  
  P = [P ; q];
end