[Eeglablist] Merging two datasets with unequal numbers of events

[Elizabeth Spencer Norton]

Hi Tarik,
Thanks for your suggestions.

Everything is the same with the two files except the length. I tried merging the data before running any Event List/Bin List procedures as part of ERPLab and that does work successfully, even with unequal numbers of events per file. However, after generating ERPLab Event Lists, the appending does not work, and I get the same error that I posted originally. After running the Event List, there are a listed number of events in the EEGLab GUI display. Everything else about the two files (sampling rate, etc.) is the same. It seems then that Event List is doing something to the urevent structure perhaps? I’m not really familiar with the idea of urevent.

My overall issue is that the two files (two runs) have the same event codes, but I want to later be able to bin the events by which run they were in so that I can create an ERP difference wave. I could keep the two runs separate and then append them once they are averaged in ERPLab, but I figured that it would be easier to do artifact detection/rejection as one file rather than two.

Thanks for any additional ideas.
Elizabeth

From: Tarik S Bel-Bahar <tarikbelbahar at gmail.com>
Reply-To: <tarikbelbahar at gmail.com>
Date: Thursday, October 27, 2016 at 2:22 PM
To: Elizabeth Spencer Norton <enorton at northwestern.edu>
Cc: "eeglablist at sccn.ucsd.edu" <eeglablist at sccn.ucsd.edu>
Subject: Re: [Eeglablist] Merging two datasets with unequal numbers of events

Hi Elizabeth, some notes below that might help. this shouldn't be a problem, and if it's repeatable please consider reporting in eeglab bugzilla.

The error of course suggests that one of your files does not have urevents, which I think are/should-be generated when a file is first loaded and saved in eeglab.
I recommend making sure that you've done the following, which should lead you past this error.

importing, epoching, and saving the two files the same way as much as possible, so there is nothing different between them except the number and type of epoch.
both files should have a "number of epochs" in the eeglab gui
both files "should" have an urevents field (unless there were no events in the file used originally?-not sure about this, see online wiki on events and urevents)
both files should have an 3-dimensional EEG.data structure
both files should have the same-length epochs
both files should already be healthily saved and re-openable in eeglab as .set files, prior to attempt at merging
both files are actively in memory as Datasets 1 and 2 (or however many datasets you're merfing.

Other than this, first two a successful mergeset and review the command that was run using eegh. Try it on two files that are copy of each of other.
You may also attempt to comment out line 275 or near there in the code to attempt to bypass the error, but this is NOT recommended unless you're matlab saavy and can read the full function code.



On Wed, Oct 26, 2016 at 2:44 PM, Elizabeth Spencer Norton <enorton at northwestern.edu<mailto:enorton at northwestern.edu>> wrote:

Hello,

I'm trying to merge (concatenate) two datasets with different numbers of events. We run an oddball paradigm with randomly selected number of standards between deviants, and this is done in two runs that have different stimuli. I'm trying to concatenate the two runs using the GUI which calls pop_mergeset, but getting the error popup "EEGLAB error in function pop_mergeset() at line 275: Reference to non-existent field 'urevent'."



Looking at the pop_mergeset script, it looks like it wants to merge the files and insert a boundary event halfway through (lines 224-228), which may be the problem with using two files of unequal length. (Using EEGLab version 13.6.5.)



I'd prefer not to just lop off events from the longer dataset to make the sizes match. If anyone has ideas for other solutions, I would appreciate it!

Best,

Elizabeth Norton

Northwestern University

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