this is to return an array of numbers that are the highest value of the arrays inside of the base array. I can get it to work when i use for statements. But I have tried to simplify it, and can't work out why it doesn't work. any help would be appriciated.

function largestOfFour(arr) {
  return arr.map((x) => x.reduce((a, c) =>  c > a ? c : a, 0));
}

let test = [[1, 2, 3][4, 5, 6][7, 8, 9]]
console.log(largestOfFour(test)) // expected output[3, 6, 9] the largest number from each array

CodePudding user response：

You don't need to reduce, you can do it by just Math.max. like this:

function findMaxNumbers(arr) {
  return arr.map((x) => Math.max(...x));
}

let test = [[1, 2, 3],[4, 5, 6],[7, 8, 9]];
console.log(findMaxNumbers(test));

CodePudding user response：

If you have values smaller than zero, you need to remove the start value

x.reduce((a, c) =>  c > a ? c : a, 0)
                                   ^

or use a very small start value, like -Number.MAX_VALUE.

CodePudding user response：

To get the max of all the maxes, you can reduce the reductions. If you just want the max's, map the reduction.

const maxOfArray = a => a.reduce((a, c) => c > a ? c : a, -Number.MAX_SAFE_INTEGER); // thanks to Nina
const conciseVLAZMax = a => Math.max(...a); // thanks to VLAZ 

let a = [
  [1, 2, 3],
  [6, -1, -2],
  [3, 4, 5],
]

let maxs = a.map(maxOfArray);
let maxMax = maxOfArray(maxs);

console.log(maxs);
console.log(maxMax);