how to group a matrix using quartile

Hello

assume I have a matrix :

a=[1 0.2;2 0.1;3 0.0002;4 2;5 1;6 0.00004;7 3;8 1.5;9 4]

b=a(:,2)

c = sort(b)

Q1 = median(c(find(c<median(c))))

percentile %25 would be 0.0501, how can i get a new matrix belong under Q1, like:

d=[3 0.0002;6 0.0004]

Thanks !

Answer 1

[Walter Roberson]

mask = b < quantile(b, 0.25);
a(mask,:)