ALLEEG & dataset management

Why do I need this step?

• ALLEEG: the shelf that holds every dataset in memory.
• EEG: the dataset you are working on now.
• CURRENTSET: the number of that dataset on the shelf.

If you do not know which dataset is current, you may filter the wrong version or save over the original. This lesson shows you how to always know where you are.

How do I do it in EEGLAB?

1. Make a change and store it as a new dataset

To have something to store, we make one simple change: remove the two eye channels EOG1 and EOG2. This is only an example for this lesson.

1. With eeglab_data.set open, open Edit › then Select data.
2. In the Channel(s) row, type EOG1 EOG2.
3. Tick the box in the same row, under on->remove these. Without this tick, EEGLAB would keep these two channels and remove all the others.
4. Click OK.
5. A window opens asking What do you want to do with the new dataset?. In Name it:, replace Continuous EEG Data with D1 no EOG.
6. Leave Save it as file: unticked. The new dataset stays in memory only.
7. Leave Overwrite it in memory (set=yes; unset=create a new dataset) unticked, so the original stays as dataset 1.
8. Click OK.

The main window now starts with #2: D1 no EOG, and Channels per frame shows 30.

2. Move between datasets

1. Open the Datasets menu. It lists Dataset 1:Continuous EEG Data and Dataset 2:D1 no EOG. The current one has a check mark.
2. Choose Dataset 1:Continuous EEG Data. The main window shows #1 and 32 channels again.
3. Any menu you use now works on dataset 1. Before each step, look at the first line of the main window to know which dataset is current.

3. Delete a dataset from memory

1. Open Edit › then Delete dataset(s) from memory.
2. In Dataset(s) to delete:, type 2.
3. Click OK. The Datasets menu now lists dataset 1 only.

Deleting from memory does not touch any file on disk. A dataset that was never saved is lost when you delete it.

How do I write it as code?

% Start EEGLAB and load the sample dataset as dataset 1
[ALLEEG, EEG, CURRENTSET, ALLCOM] = eeglab;
sampleFolder = fullfile(fileparts(which('eeglab')), 'sample_data');
EEG = pop_loadset('filename', 'eeglab_data.set', 'filepath', sampleFolder);
[ALLEEG, EEG, CURRENTSET] = eeg_store(ALLEEG, EEG, 0);

% Remove the two eye channels and store the result as a new dataset
EEG = pop_select(EEG, 'rmchannel', {'EOG1', 'EOG2'});
[ALLEEG, EEG, CURRENTSET] = pop_newset(ALLEEG, EEG, CURRENTSET, ...
    'setname', 'D1 no EOG', 'gui', 'off');

CURRENTSET                            % 2
[ALLEEG(1).nbchan ALLEEG(2).nbchan]   % 32 30

% Go back to dataset 1
[ALLEEG, EEG, CURRENTSET] = pop_newset(ALLEEG, EEG, CURRENTSET, 'retrieve', 1);
EEG.nbchan                            % 32

% Delete dataset 2 from memory (its file, if any, is not touched)
ALLEEG = pop_delset(ALLEEG, 2);
eeglab redraw;

• pop_newset with CURRENTSET stores the changed EEG as a new dataset after the current one. With 'gui', 'off' it does not open the naming window.
• 'retrieve', 1 makes dataset 1 the current dataset again, as choosing it from the Datasets menu does.

Which value should I choose?

The choice is in the window that opens after each step:

A good habit: give each version a name that says what was done, such as D1 no EOG or D1 filtered 1Hz. A dataset list full of Continuous EEG Data is easy to mix up.

How do I check it worked?

1. After step 1, the first line of the main window is #2: D1 no EOG, with 30 channels.
2. The Datasets menu lists two datasets, with a check mark on the current one.
3. After switching to dataset 1, the main window shows #1 and 32 channels.
4. After deleting, the Datasets menu lists dataset 1 only.

Nothing in this lesson is saved to disk, and the sample file stays as it was.

What mistakes do people make?

• Working on the wrong dataset. After you switch from the Datasets menu, every step applies to the dataset you chose. Check the # number in the first line of the main window before each step.
• Thinking that storing in memory saves the file. A new dataset lives in memory until you save it. It is lost when you close MATLAB.
• Forgetting the tick under on->remove these. Without it, Edit › then Select data keeps only EOG1 and EOG2, and the new dataset has 2 channels instead of 30.
• Changing EEG in a script and forgetting eeg_store or pop_newset. The change is in the EEG variable only, and the Datasets menu does not know about it.

Going further

• EEGLAB Tutorial: https://eeglab.org/tutorials/03_Dataset_management/datasets.html (3. Dataset management)