Get sub sets from list

[asaffff]

Hi,
Does anybody can tell me how can I select all sub set from list.
it means that if i have a list that contains values {1,2,3,4}
I want to get all those sub list
{1,2,3,4,12,13,14,23,24,34,123,124,234,1234}
I try to make it in many ways but it fails again and again.
code sample can help very much.
Thanks.

[dglienna]

Search for COMBINATION'S. A simple loop can compute what you want.

[BioPhysEngr]

This sounds like homework, so I'll try to only sketch the solution:

For a set of N elements there are 2^N subsets (or 2^N - 1, if you don't include the null set). An insight is that you can order them by assigning each subset a binary number. For, for the set {1, 2, 3, 4} you can denote the subset that includes the 2nd and 4th element as:

{ 2, 4 } = 0101

And in binary 0101 is 5, so this set corresponds to the number 5 and an element is included if there is a ONE at it's position in the binary representation of the number.

You can perform a loop to see if you should include an element like:

int subsetIDNumber = 0101;
for(int i = 0; i < 4; i++)
{
    if( subsetIDNumber & 1 == 1 )
        //Include the element
    else
        //Don't include the element

    subsetIDNumber >>= 1;  //Bitwise shift the subsetIDnumber right
}

Thus you can loop over them like...

int twoToTheNumElements = 16;
for(int i = 1; i <= twoToTheNumElements; i++)
{
    //Construct the subset corresponding to the number i
}

Hope that helps. Good luck.