MATLAB: How to get the FFT of a PRC file

Question

I have a code to plot information by extracting a file

    % %%


clear
[filename, pathname] = uigetfile('*.raw;*.prc', 'Pick raw or processed data file');
N=str2double(filename(5:6));
    % load processed file
    fid = fopen([pathname filename],'r','b');
    A= fread(fid,inf,'*single')';
    prcdata=reshape(A,N,[])';
    plot((1:size(prcdata,1))./1.16E6, prcdata (:,6))
   title(strrep(filename,'_','-'))
   fclose(fid);

I want to plot the FFT (fast fourier transform) of the data I plotted in the above code. I tried the following code

% %%
clear
  plot(fft(1:size(prcdata,1))./1.16E6, prcdata (:,6))

and also

% %%
y= (prcdata (:,6)); 
z= fft(y); 
plot z;

But none seem to be working I want to exchange the plot I obtained with the plot for the FFT for the same

Answer 1

y= prcdata(:,6); x=1:size(prcdata,1); z= fft(y); plot(x,z);