How do I duplicate a row in a randomly ordered array?

I am creating a moving square-wave grating to act as a visual stimulus that loops through an array of randomly ordered spatial frequency (SF) and temporal frequency (TF) in two opposite directions. I currently have the stimulus such that every time one row of the array is presented, the next one is of a random other combination of frequencies and another direction (which could be the same or the opposite). The change I want to make is that I want each combination of frequencies to be played in both directions sequentially instead of at some other random point in the array. So for example, instead of a stimulus with TF = 1, SF = 1, and Direction = 180 followed by TF = 3, SF = 3, Direction = 180. I want the stimulus to play the TF=1, SF=1, Direction = 180, followed by TF=1, SF=1, Direction=360, then onto the next random frequency combination.

Here is my code for the stim_grid, which is the randomly ordered array of frequency and direction:

%Temporal frequency vector temp_freq = [0.031,0.125,0.5,2,8,16]; %Spatial frequency vector spat_freq = [0.000657,0.001336,0.002651,0.0053,0.0106,0.0212];%calculated using trigonometry and the width of the %stimulus computer in cm spatemp_array = combvec(temp_freq,spat_freq);

%%Make array column 1 = TF, column 2 = SF, column 3 = direction stim_grid = [ repmat(spatemp_array',2,1),[repmat(stim_dir(1),length(spatemp_array'),1); repmat(stim_dir(2),length(spatemp_array'),1)] ]; %Make first pair of TF, SF, and direction stim_grid = [stim_grid(randperm(length(stim_grid)),1:3)];

Answer 1

[Jos (10584)]

A suggestion:

[SF, TF, D] = ndgrid([1 2 3], [10 20 30 40], [180 360]) % combinations three spatial and four temporal frequencies, and TWO directions
M = [SF(:) TF(:) D(:)]  % ordered list
N = size(M,1)/2 
ridx = randperm(N)
ridx = [ridx ; ridx+N]
Mfinal = M(ridx,:)

[Graham Smyth]

Thank you!