I have two arrays:

address[ ] addresses
uint [ ] numbers

I want to create a function that creates another array that stores the hashed value of both.

bytes32[ ] addressNumbers

for instance, if I have two addresses stored and two uints:

address[address1, address2] addresses,
uint [1, 2] numbers.

I want to hash them with keccak256(address, uint) such that i get an array:

bytes 32[ address1,1 ,address1,2 , address2,1 , address2,2 ] 

I assume I need to use a nested for loop, but i am having trouble figuring out how. can any of you help me put?

  • Needs adaptation to the way Ethereum works. What are you going to do with the hashes? Commented Apr 11, 2017 at 20:46
  • it is in relation to another question on here: ethereum.stackexchange.com/questions/13994/… i want to join the two arrays to create voterIssues for each voter on each issue.
    – Mads
    Commented Apr 11, 2017 at 21:00

1 Answer 1


What you can do is treat it as a many-to-many join between two tables, Voters and Issues. The relationship is usually addressed with a third table, in this case Vote (or Ballet if it reduces confusion).

In summary, push Voters and Issues into tables (arrays, or mappings with indexes). Some patterns here: Are there well-solved and simple storage patterns for Solidity?

Pick a pattern that lets you easily confirm a Voter is actually registered and an Issue actually exists. Then hash the keys and push a Vote into the Vote table.

By "table" I mean one of the constructs described in the above-linked answer. Think about the strengths a weaknesses and choose accordingly. For the votes themselves, I would consider:

struct Vote {
  bool yayNay;
  bool isVote;

mapping(she3HashKey => Vote) voteStructs;

The second field would be set to true for all votes cast so you can tell a real "false" from a default 0, because ...

In my approach, you need simple functions to check if things exist:

isVoter() public constant returns(bool isIndeed) {}
isIssue() public constant returns(bool isIndeed) {}
isVote()  public constant returns(bool isIndeed) {}

That's a must or you might get tangled up in awkward problems, e.g. differentiating a default (false) from an actual "Nay".

Check the first two before you allow a new Vote.

if(!isVoter(msg.sender)) throw;
if(!isIssue(issueId)) throw;
// continue ... 

Check the third one before you do anything with a stored Vote.

Keep your tallies as you go so you can avoid iteration at all costs.

Hope it helps.

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