Solidity Arrays – Shuffle Array of Integers in Solidity

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I have an array of integers like this,

uint256[] public numberArr = [0,0,1,1,1,1,1,1,2,2,2,2,2,3,3,3,3,4,5,5,5]

What can be the best way to shuffle this array in solidity

Best Answer

Try this:

function shuffle() external {
    for (uint256 i = 0; i < numberArr.length; i++) {
        uint256 n = i + uint256(keccak256(abi.encodePacked(block.timestamp))) % (numberArr.length - i);
        uint256 temp = numberArr[n];
        numberArr[n] = numberArr[i];
        numberArr[i] = temp;
    }
}

Related Solutions

Solidity – How to Convert String of Integers Separated by a Delimiter to Integer Array

You may use a library like stringutils or solidity-util to for that. For your special case, casting the string to bytes and manipulating like the following function will work.

contract MyContract{

    bytes tempNum ; //temporarily hold the string part until a space is recieved
    uint[] numbers;

    function splitStr(string str, string delimiter) constant returns (int []){ //delimiter can be any character that separates the integers 

        bytes memory b = bytes(str); //cast the string to bytes to iterate
        bytes memory delm = bytes(delimiter); 

        for(uint i; i<b.length ; i++){          

            if(b[i] != delm[0]) { //check if a not space
                tempNum.push(b[i]);             
            }
            else { 
                numbers.push(parseInt(string(tempNum))); //push the int value converted from string to numbers array
                tempNum = "";   //reset the tempNum to catch the net number                 
            }                
        }

        if(b[b.length-1] != delm[0]) { 
           numbers.push(parseInt(string(tempNum)));
        }
        return numbers;
    }
}

If you can't use parseInt you may use your own function to convert to uint as follow found here,

function bytesToUint(bytes b) constant returns (uint result) {

    result = 0;
    for (uint i = 0; i < b.length; i++) { 
        if (b[i] >= 48 && b[i] <= 57) {
            result = result * 10 + (uint(b[i]) - 48); 
        }
    }
    return result;
    }

Then instead of numbers.push(parseInt(string(tempNum))); you can use numbers.push(bytesToUint(tempNum));

Or you can look into the libraries code and use only the function you need. Those might be efficient.

Hope this helps!

Solidity – Returning an Uint Array with Gas and Cost Efficiency Solutions

It really depends. There are two ways of calling functions from a smart contract

Call them from an Ethereum transaction. This will call the function on-chain and cost you gas from the execution.
Call them read-only without creating a transaction. This costs no gas. This can be done because, since it's a constant function and doesn't modify the state, it can be called without creating an on-chain transaction. This wont work for functions that modify the state because the state wont persist since there is no transaction. This is usually done in web3 by doing call() on the function.

Best Answer

Related Solutions

Solidity – How to Convert String of Integers Separated by a Delimiter to Integer Array

Solidity – Returning an Uint Array with Gas and Cost Efficiency Solutions

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