palm_swapfmt.m

function Pnew = palm_swapfmt(Pset)
% Convert a set of permutation matrices to an array
% of permutation indices and vice versa.
%
%         Cell array <===> Shuffling indices
%  Shuffling indices <===> Cell array
% 
% Pnew = palm_swapfmt(Pset)
% 
% Pset : Set of permutations, sign-flips or both.
%        This can be supplied either as a cell array
%        of (sparse) permutation matrices, or an
%        array of permutation indices.
% Pnew : The converted set of permutations.
% 
% _____________________________________
% Anderson M. Winkler
% FMRIB / University of Oxford
% Dec/2013
% http://brainder.org

% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
% PALM -- Permutation Analysis of Linear Models
% Copyright (C) 2015 Anderson M. Winkler
% 
% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% any later version.
% 
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
% 
% You should have received a copy of the GNU General Public License
% along with this program.  If not, see <http://www.gnu.org/licenses/>.
% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

if iscell(Pset),
    Pnew = zeros(size(Pset{1},1),numel(Pset));
    I = (1:size(Pset{1},1))';
    for p = 1:numel(Pset),
        Pnew(:,p) = Pset{p}*I;
    end
    if size(unique(abs(Pnew)','rows'),1) == 1;
        Pnew = sign(Pnew);
    end
else
    P = speye(size(Pset,1));
    Pnew = cell(size(Pset,2),1);
    for p = 1:size(Pset,2),
        sgn = sign(Pset(:,p));
        idx = abs(Pset(:,p));
        if all(true(size(idx)) == idx),
            Pnew{p} = sparse(diag(sgn));
        else
            Pnew{p} = sparse(diag(sgn))*P(idx,:);
        end
    end
end