sortMe.sol

    // The shuffle algorithm gets the position of an object from shufflingIndex, using a random number generator, 
    // and then updates the index so that the same position cannot be given to another object

    mapping(uint => uint[2]) shufflingIndex;
    uint totalSorted;
    mapping(address => uint) pseudonymID;
    mapping(uint => address) pseudonymIndex;

    function sortMe() atTime(State.interlude, State.pseudonymEvent) {
        require(pseudonymID[msg.sender] == 0);
        totalSorted++;
        pseudonymID[msg.sender] = totalSorted;
        pseudonymIndex[totalSorted] = msg.sender;
        entropy = generateRandomNumber(entropy);
        // Map even and uneven numbers in separate indices, each integer representing a pair with two people
        // this lets people who opt-in "hitch-hike" on the shuffling of the entire population, so that optIn()
        // can be invoked continuously      
        if(totalSorted % 2 == 0) {
            uint randomNumber = 1 + (entropy % totalSorted/2);
            shufflingIndex[randomNumber][1] = totalSorted/2;
            shufflingIndex[totalSorted/2][1] = randomNumber;
        }
        if(totalSorted % 2 == 1) {
            uint randomNumber = 1 + (entropy % (totalSorted+1)/2);
            shufflingIndex[randomNumber][0] = (totalSorted+1)/2;
            shufflingIndex[(totalSorted+1)/2][0] = randomNumber;
        }
    }