Try this?
column_count = 100; % your columns
row_count = 200; % your rows
percentage_to_take = 0.2; % you take 20% of total
total_count = column_count * row_count; % total count of samples
samples_to_take = percentage_to_take * total_count;
% Use a for loop
sample = zeros(1, saamples_to_take);
for i=1:samples_to_take
c_index = randi(column_count, 1); % a random index into columnn
r_index = randi(row_count, 1); % a random index into row
% access your table
sample(i) = your_table(c_index, r_index);
end
