ft_redefinetrial.m

function [data] = ft_redefinetrial(cfg, data)

% FT_REDEFINETRIAL allows you to adjust the time axis of your data, i.e. to
% change from stimulus-locked to response-locked. Furthermore, it allows
% you to select a time window of interest, or to resegment your long trials
% into shorter fragments.
%
% Use as
%   [data] = ft_redefinetrial(cfg, data)
% where the input data should correspond to the output of FT_PREPROCESSING and the
% configuration should be specified as explained below. Note that some options are
% mutually exclusive. If you want to use both,  you neew two calls to this function
% to avoid confusion about the order in which they are applied.
%
% For selecting a subset of trials you can specify
%   cfg.trials    = 'all' or a selection given as a 1xN vector (default = 'all')
%
% For selecting trials with a minimum length you can specify
%   cfg.minlength = length in seconds, can be 'maxperlen' (default = [])
%
% For realiging the time axes of all trials to a new reference time
% point (i.e. change the definition for t=0) you can use the following
% configuration option
%   cfg.offset    = single number or Nx1 vector, by how many samples should the 
%                   time axes be shifted. i.e. if you want t=1 to be the new t=0,
%                   set cfg.offset = -1*Fs (Fs is the sampling frequency in Hz).
%                   If cfg.trials is defined, N must be equal to the original
%                   number of trials or to the number of selected trials.
%
% For selecting a specific subsection within trials (i.e. cut out a time window
% of interest) you can use the following configuration option
%   cfg.toilim    = [tmin tmax], latency window in seconds, can be
%                   Nx2 vector. If cfg.trials is defined, N must be equal
%                   to the original number of trials or to the number of 
%                   selected trials.
%
% Alternatively you can specify the begin and end sample in each trial
%   cfg.begsample = single number or Nx1 vector, expressed in samples relative
%                   to the start of the input trial. If cfg.trials is defined, 
%                   N must be equal to the original number of trials or to the
%                   number of selected trials.
%   cfg.endsample = single number or Nx1 vector, expressed in samples relative
%                   to the start of the input trial. If cfg.trials is defined, 
%                   N must be equal to the original number of trials or to the
%                   number of selected trials.
%
% Alternatively you can specify a new trial definition, expressed in
% samples relative to the original recording
%   cfg.trl       = Nx3 matrix with the trial definition, see FT_DEFINETRIAL
%
% Alternatively you can specify the data to be cut into (non-)overlapping
% segments, starting from the beginning of each trial. This may lead to loss
% of data at the end of the trials
%   cfg.length    = number (in seconds) that specifies the length of the required snippets
%   cfg.overlap   = number between 0 and 1 (exclusive) specifying the fraction of overlap between snippets (0 = no overlap)
%
% Alternatively you can merge or stitch pseudo-continuous segmented data back into a
% continuous representation. This requires that the data has a valid sampleinfo field
% and that there are no jumps in the signal in subsequent trials (e.g. due to
% filtering or demeaning). If there are missing segments (e.g. due to artifact
% rejection), the output data will have one trial for each section where the data is
% continuous.
%   cfg.continuous = 'yes'
%
% To facilitate data-handling and distributed computing you can use
%   cfg.inputfile   =  ...
%   cfg.outputfile  =  ...
% If you specify one of these (or both) the input data will be read from a *.mat
% file on disk and/or the output data will be written to a *.mat file. These mat
% files should contain only a single variable, corresponding with the
% input/output structure.
%
% See also FT_DEFINETRIAL, FT_RECODEEVENT, FT_PREPROCESSING

% Copyright (C) 2006-2021, 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;

% do the general setup of the function
ft_defaults
ft_preamble init
ft_preamble debug
ft_preamble loadvar data
ft_preamble provenance data

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

% store original datatype
dtype = ft_datatype(data);

% deal with the special case of timelock rpt_chan_time with 1 trial
oneRptTimelock = (strcmp(dtype, 'timelock') && ...
  strcmp(data.dimord, 'rpt_chan_time') && ...
  size(data.trial, 1) == 1);

% check if the input data is valid for this function, this will convert it to raw if needed
data = ft_checkdata(data, 'datatype', {'raw+comp', 'raw'}, 'feedback', 'yes');

% check if the input cfg is valid for this function
cfg = ft_checkconfig(cfg, 'forbidden',  {'trial'}); % prevent accidental typos, see issue 1729

% set the defaults
cfg.offset       = ft_getopt(cfg, 'offset',     []);
cfg.toilim       = ft_getopt(cfg, 'toilim',     []);
cfg.begsample    = ft_getopt(cfg, 'begsample',  []);
cfg.endsample    = ft_getopt(cfg, 'endsample',  []);
cfg.minlength    = ft_getopt(cfg, 'minlength',  []);
cfg.trials       = ft_getopt(cfg, 'trials',     'all', 1);
cfg.feedback     = ft_getopt(cfg, 'feedback',   'yes');
cfg.trl          = ft_getopt(cfg, 'trl',        []);
cfg.length       = ft_getopt(cfg, 'length',     []);
cfg.overlap      = ft_getopt(cfg, 'overlap',    0);
cfg.continuous   = ft_getopt(cfg, 'continuous', 'no');

% select trials of interest
if ~strcmp(cfg.trials, 'all')
  if islogical(cfg.trials)
    ft_info('selecting %d trials\n', sum(cfg.trials));
  else
    ft_info('selecting %d trials\n', length(cfg.trials));
  end
  
  % If the user made a selection of trials but gave method parameters for 
  % all original trials, keep only the selection of the parameters
  if length(cfg.offset)>1 && length(cfg.offset)==length(data.trial)
    cfg.offset = cfg.offset(cfg.trials);
  end
  if length(cfg.begsample)>1 && length(cfg.begsample)==length(data.trial)
    cfg.begsample = cfg.begsample(cfg.trials);
  end
  if length(cfg.endsample)>1 && length(cfg.endsample)==length(data.trial)
    cfg.endsample = cfg.endsample(cfg.trials);
  end
  if size(cfg.toilim, 1)>1 && size(cfg.toilim, 1)==length(data.trial)
    cfg.toilim = cfg.toilim(cfg.trials, :);
  end
  
  % select trials of interest
  tmpcfg = keepfields(cfg, {'trials', 'showcallinfo', 'trackcallinfo', 'trackusage', 'trackdatainfo', 'trackmeminfo', 'tracktimeinfo', 'checksize'});
  data   = ft_selectdata(tmpcfg, data);
  % restore the provenance information
  [cfg, data] = rollback_provenance(cfg, data);
end

Ntrial = numel(data.trial);

% check the input arguments, only one method for processing is allowed
numoptions = ~isempty(cfg.toilim) + ~isempty(cfg.offset) + (~isempty(cfg.begsample) || ~isempty(cfg.endsample)) + ~isempty(cfg.trl) + ~isempty(cfg.length) + istrue(cfg.continuous);
if numoptions>1
  ft_error('you should specify only one of the options for redefining the data segments');
end
if numoptions==0 && isempty(cfg.minlength) && strcmp(cfg.trials, 'all')
  ft_error('you should specify at least one configuration option');
end

% check that the number of chosen trials matches the number of method parameters provided
if length(cfg.offset)>1 && length(cfg.offset)~=Ntrial
  ft_error('inconsistent number of trials and offsets');
end
if length(cfg.begsample)>1 && length(cfg.begsample)~=Ntrial
  ft_error('inconsistent number of trials and begsamples');
end
if length(cfg.endsample)>1 && length(cfg.endsample)~=Ntrial
  ft_error('inconsistent number of trials and begsamples');
end
if size(cfg.toilim, 1)>1 && size(cfg.toilim, 1)~=Ntrial
  ft_error('inconsistent number of trials and toilims');
end

% start processing
if ~isempty(cfg.toilim)
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  % select a latency window from each trial
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  
  if numel(cfg.toilim) == 2
    % specified as single [tstart tend] vector
    % expand into Ntrial X 2
    cfg.toilim = repmat(cfg.toilim(:)', Ntrial, 1);
  end
  
  begsample = zeros(Ntrial,1);
  endsample = zeros(Ntrial,1);
  skiptrial = false(Ntrial,1);
  for i=1:Ntrial
    if cfg.toilim(i,1)>data.time{i}(end) || cfg.toilim(i,2)<data.time{i}(1)
      begsample(i) = nan;
      endsample(i) = nan;
      skiptrial(i) = true;
    else
      begsample(i) = nearest(data.time{i}, cfg.toilim(i,1));
      endsample(i) = nearest(data.time{i}, cfg.toilim(i,2));
      data.trial{i} = data.trial{i}(:, begsample(i):endsample(i));
      data.time{i}  = data.time{i} (   begsample(i):endsample(i));
    end
  end
  
  % also correct the sample information
  if isfield(data, 'sampleinfo')
    data.sampleinfo(:, 1) = data.sampleinfo(:, 1) + begsample - 1;
    data.sampleinfo(:, 2) = data.sampleinfo(:, 1) + endsample - begsample;
  end
  
  data.time     = data.time(~skiptrial);
  data.trial    = data.trial(~skiptrial);
  if isfield(data, 'sampleinfo'),  data.sampleinfo  = data.sampleinfo(~skiptrial, :); end
  if isfield(data, 'trialinfo'),   data.trialinfo   = data.trialinfo(~skiptrial, :);  end
  ft_info('removing %d trials in which no data was selected\n', sum(skiptrial));
  
elseif ~isempty(cfg.offset)
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  % shift the time axis from each trial
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  offset = cfg.offset(:);
  offset = round(offset); % this is in samples and hence it must be expressed as integers
  if length(cfg.offset)==1
    offset = repmat(offset, Ntrial, 1);
  end
  for i=1:Ntrial
    data.time{i} = data.time{i} + offset(i)/data.fsample;
  end
  
elseif ~isempty(cfg.begsample) || ~isempty(cfg.endsample)
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  % select a latency window from each trial based on begin and/or end sample
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  begsample = cfg.begsample(:);
  endsample = cfg.endsample(:);
  if length(begsample)==1
    begsample = repmat(begsample, Ntrial, 1);
  end
  if length(endsample)==1
    endsample = repmat(endsample, Ntrial, 1);
  end
  for i=1:Ntrial
    data.trial{i} = data.trial{i}(:, begsample(i):endsample(i));
    data.time{i}  = data.time{i} (   begsample(i):endsample(i));
  end
  
  % also correct the sampleinfo
  if isfield(data, 'sampleinfo')
    sampleinfo = data.sampleinfo(:, 1);
    data.sampleinfo(:, 1) = sampleinfo(:, 1) + begsample - 1;
    data.sampleinfo(:, 2) = sampleinfo(:, 1) + endsample - 1;
  end
  
elseif ~isempty(cfg.trl)
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  % select new trials from the existing data
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  if ischar(cfg.trl)
    % load the trial information from file
    newtrl = loadvar(cfg.trl, 'trl');
  else
    newtrl = cfg.trl;
  end
  
  % ensure that sampleinfo is present, otherwise ft_fetch_data will crash
  data = ft_checkdata(data, 'hassampleinfo', 'yes');
  
  % make a copy of the old data
  dataold = data;
  
  % make the header
  hdr = ft_fetch_header(dataold);
  
  % start with a completely new data structure
  data          = keepfields(dataold, {'cfg' 'fsample' 'label' 'topo' 'topolabel' 'unmixing' 'mixing' 'grad' 'elec' 'opto'}); % account for all potential fields to be copied over
  data.hdr      = hdr;
  data.trial    = cell(1,size(newtrl,1));
  data.time     = cell(1,size(newtrl,1));
  
  if isfield(dataold, 'trialinfo')
    ft_warning('Original data has trialinfo, using user-specified trialinfo instead');
  end
  
  if ~istable(newtrl)
    begsample = newtrl(:,1);
    endsample = newtrl(:,2);
    offset    = newtrl(:,3);
  else
    begsample = newtrl.begsample;
    endsample = newtrl.endsample;
    offset    = newtrl.offset;
  end
  trllength = endsample - begsample + 1;
  
  for iTrl=1:size(newtrl, 1)
    
    data.trial{iTrl} = ft_fetch_data(dataold, 'header', hdr, 'begsample', begsample(iTrl), 'endsample', endsample(iTrl), 'chanindx', 1:hdr.nChans, 'skipcheckdata', 1);
    data.time{iTrl}  = offset2time(offset(iTrl), dataold.fsample, trllength(iTrl));
    
    % The following ensures correct handling of trialinfo.
    
    % Determine which old trials are present in new trials
    iTrlorig = find(begsample(iTrl) <= dataold.sampleinfo(:,2) & endsample(iTrl) >= dataold.sampleinfo(:,1));
    
    if size(newtrl,2)>3 % In case user specified additional trialinfo
      data.trialinfo(iTrl,:) = newtrl(iTrl,4:end);
    elseif isfield(dataold,'trialinfo') % If old data has trialinfo
      if (numel(iTrlorig) == 1 ...      % only 1 old trial to copy trialinfo from, or
          || size(unique(dataold.trialinfo(iTrlorig,:),'rows'),1)) ... % all old trialinfo rows are identical
          && ~any(diff(dataold.sampleinfo(:,1))<=0) % and the trials are consecutive segments
        data.trialinfo(iTrl,:) = dataold.trialinfo(iTrlorig(1),:);
      else
        ft_error('Old trialinfo cannot be combined into new trialinfo, please specify trialinfo in cfg.trl(:,4)');
      end
    end
  end % for iTrl
  
  % adjust the sampleinfo in the output
  if isfield(dataold, 'sampleinfo')
    % adjust the sample information
    data.sampleinfo  = [begsample endsample];
  end
  
elseif ~isempty(cfg.length)
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  % cut the existing trials into segments of the specified length
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  data = ft_checkdata(data, 'hassampleinfo', 'yes');
  
  % create dummy trl-matrix and recursively call ft_redefinetrial
  nsmp    = round(cfg.length*data.fsample);
  nshift  = round((1-cfg.overlap)*nsmp);

  if nshift<=0
    ft_error('the overlap is too large');
  end
 
  newtrl = zeros(0,4);
  for k = 1:numel(data.trial)
    begsample = data.sampleinfo(k,1);
    endsample = data.sampleinfo(k,2);
    offset    = time2offset(data.time{k}, data.fsample);
    thistrl   = (begsample:nshift:(endsample+1-nsmp))';
    if ~isempty(thistrl) % the trial might be too short
      thistrl(:,2) = thistrl(:,1) + nsmp - 1;
      thistrl(:,3) = thistrl(:,1) + offset - thistrl(1,1);
      thistrl(:,4) = k; % keep the trial number in the 4th column, this is needed further down
      newtrl = cat(1, newtrl, thistrl);
    end
  end
  clear begsample endsample offset
  
  tmpcfg = keepfields(cfg, {'feedback', 'showcallinfo', 'trackcallinfo', 'trackusage', 'trackdatainfo', 'trackmeminfo', 'tracktimeinfo', 'checksize'});
  tmpcfg.trl = newtrl;
  
  if isfield(data, 'trialinfo') && ~istable(data.trialinfo)
    % replace the trial number with the original trial information
    tmpcfg.trl = [newtrl(:,1:3) data.trialinfo(newtrl(:,4),:)];
  elseif isfield(data, 'trialinfo') && istable(data.trialinfo)
    % construct the trl matrix as a table
    begsample = newtrl(:,1);
    endsample = newtrl(:,2);
    offset    = newtrl(:,3);
    tmpcfg.trl = [table(begsample, endsample, offset) data.trialinfo(newtrl(:,4),:)];
  elseif ~isfield(data, 'trialinfo')
    % discard the trial number
    tmpcfg.trl = newtrl(:,1:3);
  end
  
  data   = removefields(data, {'trialinfo'}); % these are in the additional columns of tmpcfg.trl
  data   = ft_redefinetrial(tmpcfg, data);
  % restore the provenance information
  [cfg, data] = rollback_provenance(cfg, data);
  
elseif istrue(cfg.continuous)
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  % identify consecutive segments that can be glued back together
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  data = ft_checkdata(data, 'hassampleinfo', 'yes');
  
  boolvec = artifact2boolvec(data.sampleinfo);
  newtrl = boolvec2trl(boolvec);
  
  % In general: An offset of 0 means that the first sample of the trial corresponds
  % to the trigger. A positive offset indicates that the first sample is later than
  % the trigger.
  
  % here we want to use the start of the recording as t=0
  newtrl(:,3) = newtrl(:,1) - 1;
  
  tmpcfg = keepfields(cfg, {'feedback', 'showcallinfo', 'trackcallinfo', 'trackusage', 'trackdatainfo', 'trackmeminfo', 'tracktimeinfo', 'checksize'});
  tmpcfg.trl = newtrl;
  
  data   = removefields(data, {'trialinfo'}); % the trialinfo does not apply any more
  data   = ft_redefinetrial(tmpcfg, data);
  % restore the provenance information
  [cfg, data] = rollback_provenance(cfg, data);
  
end % processing the realignment or data selection

if ~isempty(cfg.minlength)
  Ntrial    = length(data.trial);
  trllength = zeros(Ntrial, 1);
  % determine the length of each trial
  for i=1:Ntrial
    trllength(i) = size(data.trial{i},2) * 1/data.fsample; % this the the DURATION of the selected samples
  end
  if ischar(cfg.minlength) && strcmp(cfg.minlength, 'maxperlen')
    minlength = max(trllength);
  else
    minlength = cfg.minlength;
  end
  % remove trials that are too short
  skiptrial = (trllength<minlength);
  %if ~isempty(trl), trl = trl(~skiptrial,:); end
  data.time  = data.time(~skiptrial);
  data.trial = data.trial(~skiptrial);
  if isfield(data, 'sampleinfo'), data.sampleinfo  = data.sampleinfo(~skiptrial, :); end
  if isfield(data, 'trialinfo'),  data.trialinfo   = data.trialinfo (~skiptrial, :); end
  ft_info('removing %d trials that are too short\n', sum(skiptrial));
end

% convert back to input type if necessary
switch dtype
  case 'timelock'
    data = ft_checkdata(data, 'datatype', 'timelock');
    if oneRptTimelock
      % deal with the special case of rpt_chan_time timelock data with one
      % repetition
      data.trial = reshape(data.avg, [1 size(data.avg)]);
      data.dimord = 'rpt_chan_time';
    end
  otherwise
    % keep the output as it is
end

% do the general cleanup and bookkeeping at the end of the function
ft_postamble debug
ft_postamble previous   data
ft_postamble provenance data
ft_postamble history    data
ft_postamble savevar    data