There are a few different ways that can do this exercise. Here is one of them:
clearvars
FILE = fullfile('C:\Users\...', '*.txt'); % Directory where the files are residing. Your data file extension, e.g.: .txt, .xlsx, .csv, etc
LIST = dir(FILE);
N = length(LIST); % N = data files
D = zeros(1e3, 1e3, N);
for ii = 1 : N
FFName = fullfile(LIST(ii).folder, LIST(ii).name);
DATA = readmatrix(FFName);
D(:, :, ii) = DATA; % NOW D contains all data from N files
end
plot() % Select and process the part of D that is necessary
You can adjust this shown loop code for three different files