function [sourceout] = ft_source2sparse(sourcein)

% FT_SOURCE2SPARSE removes the grid locations outside the brain from the source

% reconstruction, thereby saving memory.

%

% This invalidates the fields that describe the grid, and also makes it

% more difficult to make a plot of each of the slices of the source volume.

% The original source structure can be recreated using FT_SOURCE2FULL.

%

% Use as

% [source] = ft_source2sparse(source)

%

% See also FT_SOURCE2FULL

% Copyright (C) 2004-2021, Robert Oostenveld

%

% This file is part of FieldTrip, see http://www.fieldtriptoolbox.org

% for the documentation and details.

%

% FieldTrip 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

% (at your option) any later version.

%

% FieldTrip 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 FieldTrip. If not, see <http://www.gnu.org/licenses/>.

%

% $Id$

% these are used by the ft_preamble/ft_postamble function and scripts

ft_revision = '$Id$';

ft_nargin = nargin;

ft_nargout = nargout;

% this function does not take a cfg as input

cfg = [];

% do the general setup of the function

ft_defaults

ft_preamble init

ft_preamble debug

ft_preamble provenance sourcein

% the ft_abort variable is set to true or false in ft_preamble_init

if ft_abort

return

end

%%

sourcein = ft_checkdata(sourcein, 'datatype', 'source', 'insidestyle', 'logical');

inside = find( sourcein.inside(:));

outside = find(~sourcein.inside(:));

fprintf('total number of dipoles : %d\n', length(inside)+length(outside));

fprintf('number of dipoles inside brain: %d\n', length(inside));

fprintf('number of dipoles outside brain: %d\n', length(outside));

%% construct the output data

% loop over parameters

fn = fieldnames(sourcein);

fn = setdiff(fn, {'dim', 'transform'});

% keep the descriptive fields that remain valid

sourceout = keepfields(sourcein, {'dim', 'transform', 'time', 'freq'});

for i=1:numel(fn)

dimord = getdimord(sourcein, fn{i});

clear tmp

if startsWith(dimord, 'pos_pos') % this should go first

tmp = sourcein.(fn{i});

tmp = tmp(inside,inside,:,:,:,:,:);

sourceout.(fn{i}) = tmp;

elseif startsWith(dimord, 'pos')

tmp = sourcein.(fn{i});

tmp = tmp(inside,:,:,:,:,:,:);

sourceout.(fn{i}) = tmp;

elseif startsWith(dimord, '{pos}')

tmp = sourcein.(fn{i});

tmp = tmp(inside);

sourceout.(fn{i}) = tmp;

elseif startsWith(dimord, '{pos_pos}')

tmp = sourcein.(fn{i});

tmp = tmp(inside,inside);

sourceout.(fn{i}) = tmp;

else

% skipping parameters with unknown dimord

end

if exist('tmp', 'var')

ft_info('making "%s" with dimord "%s" sparse', fn{i}, dimord);

else

ft_info('skipping "%s" with dimord "%s"', fn{i}, dimord);

end

end % for each field

%% do the general cleanup and bookkeeping at the end of the function

ft_postamble debug

ft_postamble previous sourcein

ft_postamble provenance sourceout

ft_postamble history sourceout