Let x be your data. Create arespective y-value which denotes grouping.
y = zeros(size(x)) ;
% get values -1.00 to -1.49
idx = x >= -1 && x < -1.49 ;
y(idx) = 1 ; % say one stand for moderate
% get values between -1.50 and -1.99
idx = x >= -1.50 && x < -1.99 ;
y(idx) = 2 ; % say two stand for
