CODEWITHSUNDEEP
matlab
will_cheuk
will_cheuk

Reputation: 379

How to obtain power set?

I would like to consider power set in my code. I want to have in each loop, I obtain a subset of {1,2,3,...,n}. For example, n=3. In the first one loop, I would like to extract the number 1 and store in a variable Index. Ultimately, I want to obtain Index=2 in the second loop, Index=3 in the third loop, Index=[1,2] in the fourth loop, Index=[1,3] in the fifth loop, Index=[2,3] in the sixth loop and , Index=[1,2,3] in the seventh loop. Of course I would like that n can be any arbitrary number, say it can be 100. I can think of listing all the cases, but are there any ways to achieve my task?

Upvotes: 0

Views: 273

Answers (1)

Yuval Harpaz
Yuval Harpaz

Reputation: 1426

nchoosk should find all k-long combinations. I suggest the following solution:

n = 3;
index = {};
for ii = 1:n
    k = nchoosek(1:n,ii);
    c = num2cell(k,2);
    index(end+1:end+length(c),1) = c;
end

Another approach is to use a binary system where 001 means that you take only 1, 011 equals [1,2], 111 equals [1,2,3] etc. Then you can get it with dec2bin with no loop:

isChosen = dec2bin(1:2^n-1) == '1';

However, if we you must have it as a cell array you loop through the rows:

index1 = {};
for ii = 1:size(isChosen,1)
    index1{ii,1} = find(isChosen(ii,:));
end

And then, if you insist on a sensible order:

[~,order] = sort(cellfun(@sum,index1));
index1 = index1(order);

Upvotes: 1

Related Questions