Soldity: Iterate through address mapping

Question

I am looking for a way to iterate through a mapping in Solidity. For example I have this mapping:

mapping (address => uint) private shares;

And I want to iterate in a function through all addresses and send them ether according to their shares.

Something like:

function giveOutEth() onlyOwner returns (bool success){
for(uint i=0; i < shares.length ; i++){
//get the address and send a value
}

}

How can I achieve this?

Thanks

Answer 1

I recieved an answer by drlecks:

contract  Holders{

uint _totalHolders; // you should initialize this to 0 in the constructor
mapping (uint=> address ) private holders;
mapping (address => uint) private shares;

function GetShares(uint shares) public {
    ... 
    holders[_totalHolders] = msg.sender;
    shares[msg.sender] = shares; 
    _totalHolders++;
    ...
} 

function PayOut() public {
    ...
    uint shares;
    for(uint i = 0 ; i<_totalHolders; i++) {
        shares = shares[holders[i]];
        ...
    }
    ... 
} 

}

but keep in mind that it will consume gas, and maybe its better that the stake holders withdraw their ETH and pay for gas themselfs.