There are a number of ways to approach this problem. One simple method is to think of using logical operators to filter out the data. I show this method below. You should be a bit careful in how you choose to filter the data using logic, as you may or may not want to include particular limit values.
data = round(100+9900*rand(2784,1));
A_lim = [100,999];
B_lim = [1e3,1499];
filt_A = data >= A_lim(1) & data <= A_lim(2);
filt_B = data >= B_lim(1) & data <= B_lim(2);
A = data(filt_A);
B = data(filt_B);
There are certainly other ways of generating the arrays A and B, such as using ismember if you generate particular values that you want to compare to, rather than ranges of values.
Hope that helps!