Requesting only a certain frequency range from FFT function

Hello all! I'm currently working on the fft function that has 1024 input data and requires only a 400 output data (400 number of lines). Below is the code I apply.

 fftGui = getappdata(0,'fftGui');
 xdata = getappdata(fftGui, 'xdata');
 graphselection = getappdata(fftGui, 'graphselection');
 L = length(handles.y);
 NFFT = L/1.28;      % e.g 800
 Y= fft(handles.y,NFFT);     
 positiveY = Y(1:((NFFT+1)/2));
 normalizedY = positiveY./(L/2);
 handles.amplitudeY = abs(normalizedY);

 deltaT = xdata(2,graphselection) - xdata(1,graphselection)
 fs = 1/deltaT
 DF = fs/size(Y,1)
 handles.freq = 0:DF:fs/2;

 plot(handles.axes2,handles.freq(1:400),handles.amplitudeY)
 grid on

The outcome produces exactly 400 number of lines as needed. However, I would like to implement where the user can apply any desired frequency range and the FFT function would perform on the time domain graph to produce the frequency domain graph only in that desired frequency range, but having 400 number of lines too.

Thanks!