Averaging Fiff-files

Simple Matlab script for averaging of Fiff-files. It assumes that all data files have identical data parameters (e.g. after interpolation).

% Compute the grand-mean for a list of Fiff-files in cell array "files{}"
% The string "file_out" specifies the file name for output
% The first file of the list will be used as a template for Fiff-output
% This obviously assumes that all files have identical parameters (e.g. are
% interpolated to a standard sensor array)
% OH, March 2009
addpath /opt/mne/matlab/toolbox/;   % fiff read/write tools
if exist('file_out')~=1,    % if not output file specified: write to current working directory
    cwd = pwd;
    file_out = fullfile( cwd, 'GrandMean.fif' );
end;
if exist('files')~=1,   % you can specify a list of files here (e.g. on-line averages for all subjects in your study)
    files = {'/fullpath/file4subj1.fif', ...
             '/fullpath/file4subj2.fif', ...
             '/fullpath/file4subj3.fif'};
end;
fid = fopen(file_out, 'a');
if fid==-1,
    fprintf(1, 'Cannot access output file %s\n', file_out);
    return;
end;
fclose(fid);
nr_files = length(files);
epoch_gm = [0];
for f = 1:nr_files, % read all files and average all that might be relevant
    fprintf(1, '%s\n', files{f});
    data = fiff_read_evoked(files{f});
    if f==1,
        data_templ = data;   % first data set will be used as template for output
    end;
    epoch_gm = epoch_gm + data.evoked.epochs;   % average MEG data epoch
end;
epoch_gm = epoch_gm/nr_files;
data_templ.evoked.epoch = epoch_gm; % insert averaged data into template structure
fiff_write_evoked(file_out, data_templ);  % Write average
% The end of this