Getting/sorting by range of numbers - syntax issue

[Rick T]

Greetings All

I'm using octave and I'm having trouble sorting out a range. I can do
the delta section by just saying include anything less than or equal
to 4. But I forget how to select a range of numbers for the Theta
section. example from 4 to 8.

Example below

%   delta 0hz to 4 hz
    array2_deltafreq_sort=sortrows(array2,1); %used only to export txt file
    array2_deltafreq_sort_limit_idx=array2_deltafreq_sort(:,1)<=4 ;%
idx to limit array

I tired

%theta 4hz to 8hz
    array2_thetafreq_sort=sortrows(array2,1); %used only to export txt file
    array2_thetafreq_sort_limit_idx=array2_thetafreq_sort(:,1)<=4 &
array2_thetafreq_sort(:,1)>=8  ;% idx to limit array to
    
array2_thetafreq_sort_limit=array2_thetafreq_sort(array2_thetafreq_sort_limit_idx,:);

but when I look at the array I get array2_thetafreq_sort_limit = [](0x8)

Any other ideas?