eeg_mergechannels.m

% EEG_MERGECHANNELS - merge the channels of two EEG structure based on 
%                     common event types latencies. This is useful for 
%                     aligning the data from 2 subjects recorded
%                     simultaneously or from 2 modalities in the same
%                     subject or to merge hyperscanning data.
% Usage:
%         >> [MERGEDEEG, EEG2PRIME] = eeg_mergechannels(EEG1, EEG2, varargin);
% Inputs:
%       EEG1 - first EEGLAB dataset
%       EEG2 - second EEGLAB dataset to be aligned with the first one. 
%
% Optional inputs:
% 'finalevents'  - ['first'|'second'|'merge'|'mergediff'] how should the
%                  final events look like. 'first' uses only the event from
%                  the first dataset. 'second' uses only the event from
%                  the second dataset after recalculating their latency.
%                  'merge' merges the events. 'mergediff' (the default)
%                  only merge the events from the second data which are not
%                  in the first one.
%
% Output:
%  MERGEDEEG  - output EEG structure with the two datasets merged. The
%               merged dataset has the same sample as EEG1 and additional
%               channels from EEG2.
%
% Example:
%  EEG1.event = struct('type', {'a' 'b' 'c' 'c' 'd' 'f' });
%  EEG2.event = struct('type', {'a' 'c' 'c' 'e' 'f' });
%  eeg_mergechannels(EEG1, EEG2)
%
% Author: Arnaud Delorme and Deepa Gupta, 2023

% Copyright (C) Arnaud Delorme, arno@ucsd.edu
%
% This file is part of EEGLAB, see http://www.eeglab.org
% for the documentation and details.
%
% Redistribution and use in source and binary forms, with or without
% modification, are permitted provided that the following conditions are met:
%
% 1. Redistributions of source code must retain the above copyright notice,
% this list of conditions and the following disclaimer.
%
% 2. Redistributions in binary form must reproduce the above copyright notice,
% this list of conditions and the following disclaimer in the documentation
% and/or other materials provided with the distribution.
%
% THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
% AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
% IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
% ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
% LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
% CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
% SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
% INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
% CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
% ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
% THE POSSIBILITY OF SUCH DAMAGE.

function [MERGEDEEG, errorvals] = eeg_mergechannels(EEG1, EEG2, varargin)

if nargin < 2
    help eeg_mergechannels
    return
end

g = finputcheck( varargin, { ...
    'eventfield1'   'string'      {}   '';
    'eventfield2'   'string'      {}   '';
    'tolerance'     'real'        {}   10;
    'verbose'       'string'      {'on' 'off'}   'on';
    'finalevents'   'string'    { 'first' 'second' 'merge' 'mergediff' }   'mergediff';
        } );
if ischar(g)
    error(g)
end

if EEG1.trials > 1 || EEG2.trials > 1
    error('The eeg_mergechannels can only process continuous data')
end

% find matching event types
% -------------------------
evenType1 = cellfun(@num2str, { EEG1.event.type }, 'uniformoutput', false);
evenType2 = cellfun(@num2str, { EEG2.event.type }, 'uniformoutput', false);

evenType1 = cellfun(@deblank, evenType1, 'uniformoutput', false);
evenType2 = cellfun(@deblank, evenType2, 'uniformoutput', false);

remainingEvents = true;
counter1 = 1;
counter2 = 1;
matchingEvents1 = [];
matchingEvents2 = [];
while counter1 <= length(EEG1.event) && counter2 <= length(EEG2.event)
    ind1 = strmatch(evenType2{counter2}, evenType1(counter1:end), 'exact');
    ind2 = strmatch(evenType1{counter1}, evenType2(counter2:end), 'exact');
    
    if length(ind1) > 1, ind1 = ind1(1); end
    if length(ind2) > 1, ind2 = ind2(1); end

    bothNonEmpty = ~isempty(ind1) && ~isempty(ind2);
    if bothNonEmpty && ind1 == 1 && ind2 == 1
        matchingEvents1 = [matchingEvents1 counter1];
        matchingEvents2 = [matchingEvents2 counter2];
        counter1 = counter1+1;
        counter2 = counter2+1;
    elseif (isempty(ind1) && ~isempty(ind2)) || (bothNonEmpty && ind2 < ind1)
        matchingEvents1 = [matchingEvents1 counter1];
        matchingEvents2 = [matchingEvents2 ind2+counter2-1];
        counter1 = counter1+1;
        counter2 = ind2+counter2;
    elseif (isempty(ind2) && ~isempty(ind1)) || (bothNonEmpty && ind1 < ind2)
        matchingEvents2 = [matchingEvents2 counter2];
        matchingEvents1 = [matchingEvents1 ind1+counter1-1];
        counter2 = counter2+1;
        counter1 = ind1+counter1;
    elseif bothNonEmpty && ind1 == ind2
        error('Issue in matching event sequences');
    else
        counter1 = counter1+1;
        counter2 = counter2+1;
    end
end        

% search for common events and count them
% ---------------------------------------
[commonEvents,ind1,ind2] = intersect(evenType1, evenType2);
if length(evenType1) - length(removeevents(evenType1, commonEvents)) > length(matchingEvents1)
    fprintf(2, 'Some common events were missed, check event structures\n');
elseif length(evenType2) - length(removeevents(evenType2, commonEvents)) > length(matchingEvents2)
    fprintf(2, 'Some common events were missed, check event structures\n');
end

event1str = evenType1(matchingEvents1);
event2str = evenType2(matchingEvents2);
if strcmpi(g.verbose, 'on')
    fprintf('Matching events structure 1 are ');
    for iEvent = 1:length(matchingEvents1)
        fprintf('%s(%d)\t', event1str{iEvent}, matchingEvents1(iEvent));
    end
    fprintf('\n');
    fprintf('Matching events structure 2 are ');
    for iEvent = 1:length(matchingEvents2)
        fprintf('%s(%d)\t', event2str{iEvent}, matchingEvents2(iEvent));
    end
    fprintf('\n');
end

% now align the two structures

% find matching fields (assuming correct orders)
% eventstruct = importevent(EEG1.event, EEG2.event, EEG1.srate)

% first change sampling rate of second input
% ------------------------------------------
latency1 = [EEG1.event(matchingEvents1).latency];
latency2 = [EEG2.event(matchingEvents2).latency];
if length(latency1) < 2
    error('At least two common events are needed to align datasets')
elseif length(latency1) == 2
    fprintf(2, 'Two common events have been found. This is enough to align the two datasets but not to check that the alignment is consistent accross all events.')
end
[~, ~, ~, slope, intercept] = fastregress(latency1, latency2);

func1to2 = @(x)x*slope+intercept;
func2to1 = @(x)(x-intercept)/slope;
latency2in1 = func2to1(latency2);

errorvals = round(abs(latency2in1-latency1));
if strcmpi(g.verbose, 'on')
    fprintf('Event offset for dataset 1 vs 2 (compare the two rows):\n')
    % show the difference
    for iEvent = 1:min(50, length(latency1))
        fprintf('%8s                    ', sprintf('%1.1f', latency1(iEvent)));
    end
    fprintf('\n');
    for iEvent = 1:min(50, length(latency2in1))
        fprintf('%8s (off by %3d ms)    ', sprintf('%1.1f', latency2in1(iEvent)), round(abs(latency2in1(iEvent)-latency1(iEvent))));
    end
end

% check alignment
flag = false;
for iEvent = 1:min(50, length(latency2in1))
    if round(abs(latency2in1(iEvent)-latency1(iEvent))) > g.tolerance
        flag = true;
    end
end
if flag
    figure; plot(latency1, latency2, '.');
    error('Alignment within %1.1f millisecond failed. Increase tolerance.', g.tolerance);
end
fprintf('\n');

% get the samples to interpolate and interpolate each channel
% -----------------------------------------------------------
samples = func1to2(1:EEG1.pnts);
MERGEDEEG = EEG1;
MERGEDEEG.data(end+EEG2.nbchan,:) = 0;
if strcmpi(g.verbose, 'on')
    fprintf('Interpolating channels:')
end
for iChan = 1:EEG2.nbchan
    MERGEDEEG.data(MERGEDEEG.nbchan+iChan,:) = interp1(1:EEG2.pnts, EEG2.data(iChan,:), samples, 'lin', 0);
    if strcmpi(g.verbose, 'on')
        fprintf('.');
    end
end
if strcmpi(g.verbose, 'on')
    fprintf('\n')
end
MERGEDEEG.nbchan = size(MERGEDEEG.data,1);

% merge channels
% --------------
if ~isempty(MERGEDEEG.chanlocs) || ~isempty(EEG2.chanlocs)
    
    if isempty(MERGEDEEG.chanlocs)
        for iChan = 1:EEG1.nbchan
            MERGEDEEG.chanlocs(iChan).labels = [ 'E' num2str(iChan) ];
        end
    end

    if isempty(EEG2.chanlocs)
        for iChan = 1:EEG2.nbchan
            EEG2.chanlocs(iChan).labels = [ 'E' num2str(iChan) ];
        end
    end

    fields = fieldnames(EEG2.chanlocs);
    for iChan = 1:length(EEG2.chanlocs)
        for iField = 1:length(fields)
            MERGEDEEG.chanlocs(EEG1.nbchan+iChan).(fields{iField}) = EEG2.chanlocs(iChan).(fields{iField});
        end
    end
end

% shift events from first dataset
% for iEvent = 1:length(MERGEDEEG.event)
%     MERGEDEEG.event(iEvent).latency = MERGEDEEG.event(iEvent).latency-9;
% end

% add events from second dataset
% ------------------------------
if ~strcmpi(g.finalevents, 'first')
    if strcmpi(g.finalevents, 'second')
        MERGEDEEG.event = [];
    elseif strcmpi(g.finalevents, 'merge')
        nonMatchingEvents2 = 1:length(EEG2.event);
    else
        nonMatchingEvents2 = setdiff(1:length(EEG2.event), matchingEvents2);
    end

        fields = fieldnames(EEG2.event);
    fields = setdiff(fields, 'latency');
    if ~isempty(nonMatchingEvents2) && isfield(EEG2.event, 'latency')
        for iEvent = nonMatchingEvents2(:)'
            MERGEDEEG.event(end+1).latency = func2to1(EEG2.event(iEvent).latency); 
            for iField = 1:length(fields)
                MERGEDEEG.event(end).(fields{iField}) = EEG2.event(iEvent).(fields{iField});
            end
        end
    end
    allLatencies = [ MERGEDEEG.event.latency ];
    if length( MERGEDEEG.event ) == length(allLatencies)
        [~,inds] = sort(allLatencies);
        MERGEDEEG.event = MERGEDEEG.event(inds);
    else
        error('Issue with empty latency field')
    end
    MERGEDEEG = eeg_checkset(MERGEDEEG, 'eventconsistency');
end

return




% legacy code using the resampling method

ratio = EEG2.srate/EEG1.srate;

initcond = [ratio latency2(1)-latency1(1)*ratio]; % srate_ratio then offset
func = @(x)mean(abs(x(1)*latency1-latency2+x(2)));
%func2 = @(x)mean(abs(ratio*latency1-latency2+x(2)));

try
    newfactor = fminsearch(@(x)func(x), initcond, optimset('MaxIter',10000));
 catch
    error('Missing function fminsearch.m - Octave users, run "pkg install -forge optim" to install missing package and try again');
end
%newfactor(2) = latency2(1)-latency1(1);
newfactor = [slope intercept];

fprintf('Ratio of sampling rate is %1.5f (%1.0f vs %1.0f) optimized to %1.5f\n', EEG2.srate/EEG1.srate, EEG1.srate, EEG2.srate, newfactor(1))
fprintf('Event offset is %1.1f samples or %1.1f seconds\n', newfactor(2), newfactor(2)/EEG2.srate)
fprintf('Event offset (compare row 1 and 2): ');


latency1corrected = (latency2 - newfactor(2))/newfactor(1);
for iEvent = 1:min(50, length(latency1))
    fprintf('%8s                    ', sprintf('%1.1f', latency1(iEvent)));
end
fprintf('\n                                    ');
for iEvent = 1:min(50, length(latency2))
    fprintf('%8s (off by %3d ms)    ', sprintf('%1.1f', latency1corrected(iEvent)), round(abs(latency1corrected(iEvent)-latency1(iEvent))));
end
fprintf('\n');

% offset raw EEG2 to match EEG1
% -----------------------------
newsrate = round(100*EEG2.srate/newfactor(1))/100;
fprintf('Resampling second dataset to %1.2f (to best match first dataset %1.1% sampling rate\n', newsrate, EEG1.srate)
TMPEEG2 = pop_resample(EEG2, newsrate);

% shift data
% ----------
originalOffset = round(newfactor(2)/newfactor(1));
fprintf('Shift origin of second dataset by %d samples to match first dataset\n', originalOffset)
if originalOffset > 0
    TMPEEG2.data(:,1:originalOffset) = [];
elseif originalOffset < 0
    TMPEEG2.data = [ zeros(TMPEEG2.nbchan, -originalOffset) TMPEEG2.data ];
end
for iEvent = 1:length(TMPEEG2.event)
    TMPEEG2.event(iEvent).latency = TMPEEG2.event(iEvent).latency - originalOffset;
end

if size(TMPEEG2.data,2) < size(EEG1.data,2)
    fprintf('Padding second dataset with %d samples so it matches the length of the first one\n', size(EEG1.data,2)-size(TMPEEG2.data,2))
    TMPEEG2.data(:,end+1:size(EEG1.data,2)) = 0;
elseif size(TMPEEG2.data,2) > size(EEG1.data,2)
    fprintf('Removing second dataset %d trailing samples so it matches the length of the first one\n', size(EEG1.data,2)-size(TMPEEG2.data,2))
    TMPEEG2.data(:,size(EEG1.data,2)+1:end) = [];
end

% merge datasets
% --------------
MERGEDEEG = EEG1;
TMPEEG2.event(matchingEvents2) = [];
MERGEDEEG.data(end+1:end+TMPEEG2.nbchan,:) = TMPEEG2.data;

fields = fieldnames(TMPEEG2.chanlocs);
inds = length(MERGEDEEG.chanlocs)+1:length(MERGEDEEG.chanlocs)+1+TMPEEG2.nbchan-1;
if ~isempty(TMPEEG2.chanlocs)
    for iField = 1:length(fields)
        [MERGEDEEG.chanlocs(inds).(fields{iField})] = deal(TMPEEG2.chanlocs.(fields{iField}));
    end
elseif ~isempty(EEG1.chanlocs)
    MERGEDEEG.chanlocs(end+length(TMPEEG2.chanlocs)).labels = '';
end

fields = fieldnames(TMPEEG2.event);
inds = length(MERGEDEEG.event)+1:length(MERGEDEEG.event)+1+length(TMPEEG2.event)-1;
if ~isempty(TMPEEG2.event)
    for iField = 1:length(fields)
        [MERGEDEEG.event(inds).(fields{iField})] = deal(TMPEEG2.event.(fields{iField}));
    end
end
MERGEDEEG = eeg_checkset(MERGEDEEG, 'eventconsistency');

% return a modified version of EEG2 with changed sampling rate and samples removed
% --------------------------------------------------------------------------------
EEG2PRIME = EEG2;
EEG2PRIME.srate = EEG1.srate*newfactor(1);

eeg2offset = round(originalOffset * newfactor(1));
if originalOffset > 0
    EEG2PRIME = pop_select(EEG2PRIME, 'rmpoint', [ 1 eeg2offset ]);
elseif originalOffset < 0
    EEG2PRIME.data = [ zeros(EEG2PRIME.nbchan, -eeg2offset) EEG2PRIME.data ];
    for iEvent = 1:length(EEG2PRIME.event)
        EEG2PRIME.event(iEvent).latency = EEG2PRIME.event(iEvent).latency + eeg2offset;
    end
end

% remove event types from list
% ----------------------------
function allevents = removeevents(allevents, rmlist)

for iEvent = 1:length(rmlist)
    inds = strmatch(allevents, rmlist{iEvent}, 'exact');
    allevents(inds) = [];
end