data_500 = rand(1, 500); % 500 random values
values_40 = randperm(500, 40); % 40 random values(2*20 items)
first_20list = data_500(values_40(1:20)); % selection first 20 items list from 500 samples
second_20list = data_500(values_40(21:end));% selection second 20 items list from 500 samples
