# concatenate\_epochs and subset of them **URL:** \ **Category:** Mailing List Archive (read-only)\ **Tags:** list-archive\ **Created:** [December 15, 2016, 1:03pm UTC](https://mne.discourse.group/t/concatenate-epochs-and-subset-of-them/1140 "2016-12-15T13:03:09Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [December 15, 2016, 1:03pm UTC](https://mne.discourse.group/t/concatenate-epochs-and-subset-of-them/1140/1 "2016-12-15T13:03:09Z")
Dear mne users, I?m dealing with a 3 blocks experiment and for each block I have a raw object. Then I?m epoching every raw object using the same event\_id = [A, B, C, D]. Later I concatenate the 3 epochs objects with: epochs\_merged = mne.concatenate\_epochs([epochs1, epochs2, epochs3]) First question, when concatenating, in the console I have the message: \*Applying baseline correction (mode: mean)\* , but in the documentation I can?t find any reference of it. Since I already used baseline correction when creating epochs1, epochs2, epochs3, could this additional correction generate any problem? Later I?m doing some processing on epochs\_merged (AutoReject, ICA). Is it possible to access a subset of epochs\_merged, for example just the epochs with the event A, and average them? Otherwise I have to re-run the analysis on a newly created epochs object with event\_id = A, but I would prefer to avoid this, since from my understanding ICA performs better with more data. Thank you in advance, LA MSc student, University of Padova -------------- next part -------------- An HTML attachment was scrubbed... URL: [http://mail.nmr.mgh.harvard.edu/pipermail/mne\_analysis/attachments/20161215/89fafb02/attachment.html](http://mail.nmr.mgh.harvard.edu/pipermail/mne_analysis/attachments/20161215/89fafb02/attachment.html) ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [December 15, 2016, 1:58pm UTC](https://mne.discourse.group/t/concatenate-epochs-and-subset-of-them/1140/2 "2016-12-15T13:58:01Z")
Hi, the first logging message is actually a bit misleading because it is only storing the baseline parameters. So the baselining actually only happens when the data is loaded (probably on concatenation in your case). If you construct the epochs by passing a dict as the event\_id (see for example [http://mne-tools.github.io/stable/auto\_tutorials/plot\_object\_epochs.html](http://mne-tools.github.io/stable/auto_tutorials/plot_object_epochs.html)), you can get a copy of the 'A' category by doing ``epochs['A']``. -Jaakko ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [December 15, 2016, 2:19pm UTC](https://mne.discourse.group/t/concatenate-epochs-and-subset-of-them/1140/3 "2016-12-15T14:19:54Z")
Hi Jaakko, that was very clear thank you! I saw that you have already commited a fix on github, awesome! Lorenzo ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [December 15, 2016, 7:35pm UTC](https://mne.discourse.group/t/concatenate-epochs-and-subset-of-them/1140/4 "2016-12-15T19:35:01Z")
Hi all, > Then I?m epoching every raw object using the same event\_id = [A, B, C, D]. > > Later I concatenate the 3 epochs objects with: > epochs\_merged = mne.concatenate\_epochs([epochs1, epochs2, epochs3]) [...] > Later I?m doing some processing on epochs\_merged (AutoReject, ICA). Is it > possible to access a subset of epochs\_merged, for example just the epochs > with the event A, and average them? > Otherwise I have to re-run the analysis on a newly created epochs object > with event\_id = A, but I would prefer to avoid this, since from my > understanding ICA performs better with more data. I would be interested in an easy solution for this issue, too. Of course one could extract these subsets of data manually, but is there maybe an easier way I have simply overlooked so far? Thanks,     Richard ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [December 15, 2016, 8:24pm UTC](https://mne.discourse.group/t/concatenate-epochs-and-subset-of-them/1140/5 "2016-12-15T20:24:54Z")
for a given epochs instance you have access to epochs.events and epochs.selection attributes. that should allow you to track what epoch correspond to what. HTH Alex ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [December 20, 2016, 12:37pm UTC](https://mne.discourse.group/t/concatenate-epochs-and-subset-of-them/1140/6 "2016-12-20T12:37:58Z")
> for a given epochs instance you have access to epochs.events and > epochs.selection attributes. > that should allow you to track what epoch correspond to what. Thanks Alex! I realized my question had already been answered by Jaakko: