How to iterate over cell array, creating only unique combinations of cells

Hello,

I have data stored in a n x n cell array. For example:

data = {[1 1 1] [2 2 2]; [3 3 3] [4 4 4]};

I want to iterate over this cell array and create all unique combinations of cells. In this case, they would be:

• [1 1 1] [2 2 2]
• [1 1 1] [3 3 3]
• [1 1 1] [4 4 4]
• [2 2 2] [3 3 3]
• [2 2 2] [4 4 4]
• [3 3 3] [4 4 4]

Please note that every combination (e.g. [1 1 1][2 2 2]) only exists once regardless of order (i.e., there is no [2 2 2][1 1 1] combination).

I have tried doing this with for loops, however, I can't get behind how to not create the second combination.

Important note: I am trying to do this with for-loops since I need a way to keep track of from which column the combination is coming from (i.e. if the two data points are from the same column --> this would apply to [1 1 1][3 3 3] and [2 2 2][4 4 4] in my example). Therefore any function which simply returns me the permutations or binary coefficient won't work.

Answer 1

[Stephen23]

data = {1,2;3,4};
n = numel(data);
m = nchoosek(1:n,2) % each row is one combination pair.

m = 6×2

1 2 1 3 1 4 2 3 2 4 3 4

●

out = data(m) % output

out = 6x2 cell array
    {[1]}    {[3]}
    {[1]}    {[2]}
    {[1]}    {[4]}
    {[3]}    {[2]}
    {[3]}    {[4]}
    {[2]}    {[4]}

[idr,idc] = ind2sub(size(data),m);
idx = ~diff(idc,1,2) % output is from the same column

idx = 6x1 logical array
   1
   0
   0
   0
   0
   1

[Phoebe Daphne]

Thank you very much, this worked.