Sum all possible combinations of tablecolumns

I have a table with 30 columns. Now i would like create new tables for all possible summations of the table columns.

Like :

• a table for all possible summations of 2 columns
• a table for all possible summations of 3 colomns
• a table for all possible summations of 4 colomns
• ...

Is there a way/ matlab function of combination of functions to realise this?

Answer 1

[KSSV]

You can get all possible combinations of k columns choosen out of given n columns using nchoosek. REad about this function. You can get the sum of columns using sum. I have give a demo of calculating sum of two coumns with all possible combinations out of give columns. This can bve extended to any of your interested case.

A = rand(10,5) ;   % matrix for demo 
[m,n] = size(A) ;  % get size of matrix 
% Get possilbe combinations out of 5 columns when 2 columns are pciked 
col = 1:n ;
idx = nchoosek(col,2) ; 
% Add all combinations of two columns pciked from A 
iwant = zeros(m,size(idx,1)) ;  % initialize the required 
for i = 1:size(idx,1)
  iwant(:,i) = sum(A(:,idx(i,:)),2) ; 
end

[Senne Van Minnebruggen]

This method works only when the number of combination is small. In my case i have a table with 30 columns. So when i would like all the possible summations of 15 columns there are (nchooske(30,15)) 155117520 possible combinations. This is causing the following errors:

Error using zeros

Requested 155117520x15 (17.3GB) array exceeds maximum array size preference. Creation of arrays greater than

this limit may take a long time and cause MATLAB to become unresponsive. See array size limit or preference

panel for more information.

Error in nchoosek>combs (line 164)

P = zeros(total, k, 'like', v);

Error in nchoosek (line 123)

c = combs(v,k);

[KSSV]

Yes it needs a huge memory.....try to run it on a pc with good RAM. Or if you have GPU card try to explore that option. It turns out to be an array of size 155117520x15. I could run it in my 4 GB machine.