how to get maximum of value between multiple keys from array

Question

how to get maximum of value between multiple keys from array?

I have tried this below method for only three(not multiple) keys.

getMaxValuefromkeys(values: any[], key1: string, key2: string, key3: string) {
    var val1 = Math.max.apply(Math, values.map(function (a) { return a[key1] }));
    var val2 = Math.max.apply(Math, values.map(function (a) { return a[key2]; }));
    var val3 = Math.max.apply(Math, values.map(function (a) { return a[key2]; }));
    if (val1 >= val2 || val1 >= val3) {
        return val1;
    } else if (val2 >= val3 || val2 >= val1) {
        return val2;
    }
    return val3;
}

---

But we need to check more condition and write more codes if we use multiple keys. So I have tried these below codes

Math.max.apply(Math, values.map(function (a) { return a[key1], a[key2], a[key3]; }));
                                         // where I want to return multiple keys 

---

But it's not working. Is any single line of code available for getting max value in between multiple keys from array?

Answer 1

Array#map each object to it's maximum value, then find the maximum of the array:

var values = [{ a: 4, b: 3 }, { a: 2, b: 8 }, { a: 1, b: 2 }];

var key1 = 'a', key2 = 'b';

var result = Math.max.apply(Math, values.map(function (a) { return Math.max(a[key1], a[key2]); }));

console.log(result);

If you want something more flexible that can accept multiple keys:

var values = [{ a: 4, b: 3, c: 23 }, { a: 2, b: 28, c: 13 }, { a: 1, b: 2, c: 1 }];

function getMaxOfKeys(values, keys) {
  return Math.max.apply(Math, values.map(function(obj) {
    return Math.max.apply(Math, keys.map(function(key) {
      return obj[key];
    }));
  }));
}

// or the ES6 equivalent

const getMaxOfKeysES6 = (values, keys) => 
  Math.max(...values.map(
    (obj) => 
      Math.max(...keys.map((key) => obj[key]))
    )
  );

console.log(getMaxOfKeys(values, ['a', 'b', 'c']));
console.log(getMaxOfKeysES6(values, ['a', 'b', 'c']));

Answer 2

(plain ES6 - I don't do TypeScript)

Given your object values and a set of keys that you wish to compare, e.g.:

let values = [
   { key1: 2, key2: 3, key3: 0 },
   { key1: 10, key2: 0, key3: 5 }
];

then for each key, find the maximal value within each object and return that as an array, and then find the maximal value of that array.

function getMaxValuefromkeys(values, ...keys) {
    return Math.max(...keys.map(key => Math.max(...values.map(o => o[key]))));
}

with usage:

let max = getMaxValuefromkeys(values, 'key1', 'key2', 'key3');

or given an array of keys:

let max = getMaxValuefromkeys(values, ...keys);