How to get an array of one key from struct array?

Question

I have a struct array like so:

struct People {
        uint256 age;
        string name;
}

People[] public peopleArray;

Is there a way I can easily get an array containing the ages of the People? The code I have now is something like:

function getPeopleAges() public view returns (uint256[] memory) {
        uint256[] memory temp = new uint256[](peopleArray.length);
        for (uint8 i = 0; i < peopleArray.length; i++) {
            temp[i] = peopleArray[i].age;
        }

        return temp;
    
}

This seems needlessly bulky, so I was wondering if there was a more simplified or better way to do this. For example, in javascript you can do something like this:

return peopleArray.map(a => a.age);

Is there a solidity equivalent to that?

Answer 1

I think a loop would be the only way to do it that way, hoewever you could just add the age to the peopleArray in the same function you add the age and name to the People struct.

Answer 2

The EVM is constrained by hard limits on execution cost. Consequently, you want to optimize thr storage layout precisely to avoid convoluted conversions like that.

You could have two arrays, one for ages and one for names, and that would get you some of the way there, but I would caution you about scalability. What happens when the arrays get large?

Scalability depends on always having an O(1) solution. Some food for thought: https://blog.b9lab.com/getting-loopy-with-solidity-1d51794622ad

Hope it helps.