How to divide Epochs object into multiple smaller ones based on the number of the epoch?

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1

MNE version: e.g. 1.3.1
operating system: Windows 11

Hello,
I have an Epoched object from a learning task. I would like to divide it so that the first 30 epochs (with the same event_id) go into one object, the second 30 into another one, and so on. I want to do this because I am interested in comparing the ERPs from different timepoints of the experiment.

Is there a way how to do this?

Thank you so much for your help.

Best wishes, Iva

2

Hello,

You can index on epochs, on both IDx and condition.

from mne import Epochs, find_events
from mne.datasets import sample
from mne.io import read_raw_fif


directory = sample.data_path() / "MEG" / "sample"
raw = read_raw_fif(directory / "sample_audvis_raw.fif", preload=False)
raw.pick_types(eeg=True, stim=True)
raw.load_data()

event_id = dict(left=1, right=2)
events = find_events(raw, stim_channel="STI 014")
epochs = Epochs(
    raw,
    events,
    event_id=event_id,
    tmin=-0.2,
    tmax=0.5,
    reject=None,
    preload=True,
)

There are 72 left epochs and 73 right epochs.

>>> epochs
<Epochs |  145 events (all good), -0.199795 - 0.499488 sec, baseline -0.199795 – 0 sec, ~34.6 MB, data loaded,
 'left': 72
 'right': 73>

To select the 30 first left epochs: epochs["left"][:30].

>>> epochs["left"][:30]
<Epochs |  30 events (all good), -0.199795 - 0.499488 sec, baseline -0.199795 – 0 sec, ~9.5 MB, data loaded,
 'left': 30>

To select the 30 first epochs, left or right: epochs[:30].

>>> epochs[:30]
<Epochs |  30 events (all good), -0.199795 - 0.499488 sec, baseline -0.199795 – 0 sec, ~9.5 MB, data loaded,
 'left': 15
 'right': 15>

And so on.

Mathieu

3 Likes
3

Thank you so much for your reply, Mathieu!