# many epochs dropped due to 'NO\_DATA' **URL:** \ **Category:** Mailing List Archive (read-only)\ **Tags:** list-archive\ **Created:** [April 7, 2016, 10:24am UTC](https://mne.discourse.group/t/many-epochs-dropped-due-to-no-data/989 "2016-04-07T10:24:41Z")\ **Posts on this page:** 4\ **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:** [April 7, 2016, 10:24am UTC](https://mne.discourse.group/t/many-epochs-dropped-due-to-no-data/989/1 "2016-04-07T10:24:41Z")
Hi, Thanks for the hint; It must have something to do with it. I must be overlooking something here, but I can't get it right: Somehow it looks as if the epochs method looks for timestamps from before the cropping of the data from somewhere (?), although I'm not sure how that is possible I first crop my data with raw.crop, save that data, and load it again from file. I previously crop the file at 232 seconds - it loses the first 44 epochs. Other files I don't crop don't have this problem. I can't figure out what's wrong about the time indices: the resulting raw structure has the correct raw.time (from 0 to 618, at sfreq=1000) and time indices: raw[0][1] goes from 0 to 618; len(raw[0][1]): 618001 My events array goes like this: In [37]: events Out[37]: array([[9279, 0, 1],        [18677, 0, 2],        [28475, 0, 3],        [38491, 0, 3],        [49491, 0, 1],        [58705, 0, 3],        [69505, 0, 1],        [79905, 0, 1],        [89736, 0, 1],        [99134, 0, 2],        [108933, 0, 1],        [118948, 0, 1],        [128146, 0, 2],        [138361, 0, 3],        [147759, 0, 2],        [157558, 0, 3],        [167774, 0, 1],        ......        [595400, 0, 1]]) Notably, I lose the first epochs, not the last epochs: epochs = mne.Epochs(raw,events, event\_id, tmin=tmin, tmax=tmax, proj=True, picks=picks\_plan2,                     baseline=None, preload=True,                     reject=None) In [35]: 60 matching events found Applying baseline correction (mode: mean) 0 projection items activated Loading data for 60 events and 1001 original time points ... 44 bad epochs dropped In [36]: epochs.drop\_log Out[36]: [['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], ['NO\_DATA'], [], [], [], [], [], [], [], [], [], [], [], [], [], [], [], []] Any Ideas? Many Thanks, cheers Tristan ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [April 7, 2016, 10:36am UTC](https://mne.discourse.group/t/many-epochs-dropped-due-to-no-data/989/2 "2016-04-07T10:36:54Z")
have a look at raw.first\_samp it can interfere. It is basically an offset in samples A ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [April 8, 2016, 12:56am UTC](https://mne.discourse.group/t/many-epochs-dropped-due-to-no-data/989/3 "2016-04-08T00:56:36Z")
That was it; when adding raw.first\_samp to all my events I lose no epochs. I guess a cleaner way is to reset the first\_samp property. For others with this problem, instead of: raw.first\_samp=0 do this (found by asking ipython for the definition with: raw.first\_samp?? ): raw.\_first\_samps[0]=0 May I suggest a switch in the crop method (e.g.: keep\_offset=True)? Thanks for the help! Tristan ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [April 8, 2016, 5:50am UTC](https://mne.discourse.group/t/many-epochs-dropped-due-to-no-data/989/4 "2016-04-08T05:50:41Z")
I'm not sure if it is a good idea to set the first\_samp property by hand. It could have some side effects elsewhere. In general, you shouldn't have to change the private attributes yourself. I don't know your analysis pipe line, but the events should line up properly if you do mne.find\_events to the cropped data. This way the events outside the cropping window will be excluded.