I thought I described it pretty clearly. Each subject has 6 trials. Each trial has up to 90 rows of data, one row for each time point (see the original post and sample data). I want to sample subjects, not rows within subjects. I need to keep the entirety of a trial together in the sampling. I can't have it taking 25% of a subjects trials, but I need 25% of the subjects. And each subject's entire length of trials needs to be retained. It's not sufficient to simply reduce each subject to one row and sample from that, which is I think what you are proposing. I need to keep the entire trial coherent and sample participants, not rows within a participant.
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