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). You should also have applied identical filtering, baseline correction, referencing etc. where appropriate.

% 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

% output file name for grand-mean data
file_out = '/fullpath/GrandMean.fif';

% List of fiff-files to be averaged
fiff_files = {'/fullpath/file4subj1.fif', ...
              '/fullpath/file4subj2.fif', ...
              '/fullpath/file4subj3.fif'};

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(fiff_files);

epoch_gm = [0];
for ff = 1:nr_files, % read all files and average all that might be relevant
    fprintf(1, '%s\n', fiff_files{ff});
    data = fiff_read_evoked(fiff_files{ff});
    if ff==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