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function [cfg] = ft_definetrial(cfg)
% FT_DEFINETRIAL defines the trials or segments of data that will be used for further
% processing and analysis, i.e. the pieces of data that will be read in by
% FT_PREPROCESSING. Trials are defined by their begin and end sample in the data file
% and each trial has an offset that defines where the relative t=0 point (usually the
% sample at which the trigger is detected) is for that trial or segment.
% Use as
% [cfg] = ft_definetrial(cfg)
% where the configuration structure should contain
% cfg.trialdef = structure with the details of trial definition, see below
% cfg.trialfun = string with the function name, see below (default = 'ft_trialfun_general')
% cfg.representation = 'numeric' or 'table', determines how the trial definition is returned (default is automatic)
% and furthermore
% cfg.dataset = string with the filename
% or
% cfg.headerfile = string with the filename
% cfg.datafile = string with the filename
% and optionally
% cfg.headerformat = string, see FT_FILETYPE (default is automatic)
% cfg.dataformat = string, see FT_FILETYPE (default is automatic)
% cfg.eventformat = string, see FT_FILETYPE (default is automatic)
% In general, a call to FT_DEFINETRIAL results in the trial definition "trl" being
% added to the output configuration. The trials are defined on the basis of events or
% triggers by a user-specified MATLAB function that is subsequently referred to as
% the trial function. The user can specify their own custom function tailored to the
% experimental paradigm, or use one of the default trial functions (see below).
% Simple trial definitions (for example based on a single trigger) are supported by
% FT_TRIALFUN_GENERAL, which is specified as the default. It supports the following
% options
% cfg.trialdef.eventtype = string, or cell-array with strings
% cfg.trialdef.eventvalue = number, string, or list with numbers or strings
% cfg.trialdef.prestim = number, latency in seconds (optional)
% cfg.trialdef.poststim = number, latency in seconds (optional)
% To read all data from a continuous file in a single or in multiple segments,
% FT_TRIALFUN_GENERAL understands the following options
% cfg.trialdef.triallength = duration in seconds (can also be 1 or Inf)
% cfg.trialdef.ntrials = number of trials (can also be 1 or Inf)
% cfg.trialdef.overlap = number between 0 and 1 (exclusive) specifying the fraction of overlap between snippets (0 = no overlap)
% To display a list with the events in your data on screen, you can use
% FT_TRIALFUN_SHOW. This is useful for diagnostics; no actual trials will be defined.
% To display a graphical user interface dialog that allows you to select events of
% interest, you can use FT_TRIALFUN_GUI.
% The trial definition "trl" is an Nx3 matrix or table, where N is the number of
% trials. The first column contains the sample-indices of the start of each trial
% relative to the start of the raw data, the second column contains the sample
% indices of the end of each trial, and the third column contains the offset of the
% trigger with respect to the trial. 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, and a negative offset indicates that the trial
% begins before the trigger.
% Besides the required three columns in the trial definition "trl" that represent
% start, end and offset, it can have contain additional columns . These additional
% columns can be used by a custom trialfun to provide information about each trial,
% such as trigger codes, response latencies, trial type and response correctness.
% After FT_PREPROCESSING these additional columns of the "trl" matrix will be
% represented in the "trialinfo" field.
% If FT_TRIALFUN_GENERAL or FT_TRIALFUN_GUI has been used to generate the "trl"
% matrix or table, the function may return a fourth column that refers to the
% event-code for the corresponding trial. Whether or not this column is returned
% depends on the acquisition system. In general, this fourth column is generated by
% default if the event codes are represented numerically, or as a string starting
% with 'S' or 'R' (for BrainVision data).
% If you need to define the segments of interest on the basis of a conditional
% sequence of events (e.g. stimulus trigger followed by a correct response) or on
% basis of some signal feature that needs to be detected in the data, you should
% supply in cfg.trialfun the name of a function that you wrote yourself and that
% FT_DEFINETRIAL will call. The function receives the cfg structure as input and
% should return a NxM matrix in the same format as "trl" as the output. You can add
% extra custom fields to cfg.trialdef to pass to your own trialfun. See below for
% pointers to some examples.
% Undocumented local options:
% cfg.datafile
% cfg.dataset
% cfg.event
% cfg.trl
% cfg.version
% Copyright (C) 2003-2021, Robert Oostenveld, FCDC
% This file is part of FieldTrip, see
% 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
% 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 <>.
% $Id$
% 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_preamble init
ft_preamble debug
ft_preamble provenance
ft_preamble trackconfig
% the ft_abort variable is set to true or false in ft_preamble_init
if ft_abort
% check if the input cfg is valid for this function
cfg = ft_checkconfig(cfg, 'dataset2files', 'yes');
% this is deprecated as of 26 Sept 2021, it can be removed in a few years
if issubfield(cfg, 'trialdef.eventtype')
if isequal(cfg.trialdef.eventtype, '?')
ft_warning('cfg.trialdef.eventtype=''?'' is deprecated, please specify cfg.trialfun=''ft_trialfun_show''');
cfg.trialfun = 'ft_trialfun_show';
cfg.trialdef = rmfield(cfg.trialdef, 'eventtype');
elseif isequal(cfg.trialdef.eventtype, 'gui')
ft_warning('cfg.trialdef.eventtype=''gui'' is deprecated, please specify cfg.trialfun=''ft_trialfun_gui''');
cfg.trialfun = 'ft_trialfun_gui';
cfg.trialdef = rmfield(cfg.trialdef, 'eventtype');
end % default based on eventtype
if issubfield(cfg, 'trialdef.eventvalue')
if isequal(cfg.trialdef.eventvalue, '?')
ft_warning('cfg.trialdef.eventvalue=''?'' is deprecated, please specify cfg.trialfun=''ft_trialfun_show''');
cfg.trialfun = 'ft_trialfun_show';
cfg.trialdef = rmfield(cfg.trialdef, 'eventvalue');
elseif isequal(cfg.trialdef.eventvalue, 'gui')
ft_warning('cfg.trialdef.eventvalue=''gui'' is deprecated, please specify cfg.trialfun=''ft_trialfun_gui''');
cfg.trialfun = 'ft_trialfun_gui';
cfg.trialdef = rmfield(cfg.trialdef, 'eventvalue');
end % default based on eventvalue
% set the default options
cfg.trialfun = ft_getopt(cfg, 'trialfun', 'ft_trialfun_general'); % the default might already be set above
cfg.representation = ft_getopt(cfg, 'representation'); % this can 'numeric' or 'table'
if isfield(cfg, 'trl')
% the trial definition is already part of the configuration
ft_info('retaining existing trial definition\n');
trl = cfg.trl;
if isfield(cfg, 'event')
ft_info('retaining existing event information\n');
event = cfg.event;
event = [];
% try to locate the trialfun
trialfunSpecified = cfg.trialfun;
cfg.trialfun = ft_getuserfun(cfg.trialfun, 'trialfun');
if isempty(cfg.trialfun)
ft_error('the specified trialfun ''%s'' was not found', trialfunSpecified);
ft_info('evaluating trial function ''%s''\n', func2str(cfg.trialfun));
% determine the number of outpout arguments of the user-supplied trial function
% the nargout function in MATLAB 6.5 and older does not work on function handles
num = nargout(cfg.trialfun);
num = 1;
if num==1
% the user-defined function only gives back the trial definition
trl = feval(cfg.trialfun, cfg);
event = [];
% the user-defined function also gives back detailed information about
% conditions, reaction time or any other information
[trl, event] = feval(cfg.trialfun, cfg);
end % if trl is present or trialfun specified
if size(trl,1)<1
if isequal(cfg.trialfun, 'ft_trialfun_show') || isequal(cfg.trialfun, str2func('ft_trialfun_show'))
% give a gentle message instead of an error
ft_notice('no trials have been defined yet, see FT_DEFINETRIAL for further help\n');
% give an error in all other cases
ft_error('no trials were defined, see FT_DEFINETRIAL for help');
elseif size(trl,2) < 3
ft_error('trl must have at least 3 columns, see FT_DEFINETRIAL for help');
% set trl to requested type
if isempty(cfg.representation)
% keep the format as is
elseif strcmp(cfg.representation, 'numeric') && istable(trl)
% convert from table to numeric
trl = table2array(trl);
elseif strcmp(cfg.representation, 'table') && isnumeric(trl)
% convert the numeric array to a table
trl = array2table(trl);
% the 3 first columns are named begsample, endsample and offset, and the rest get default names
trl.Properties.VariableNames(1:3) = {'begsample', 'endsample', 'offset'};
% add the events to the output configuration
if isstruct(event)
ft_info('found %d events\n', length(event));
cfg.event = event;
elseif istable(event)
ft_info('found %d events\n', size(event, 1));
cfg.event = event;
% add the trial definition to the output configuration
if size(trl,1)>0
ft_info('created %d trials\n', size(trl,1));
cfg.trl = trl;
% do the general cleanup and bookkeeping at the end of the function
ft_postamble trackconfig
ft_postamble provenance
ft_postamble debug