Get max values from each array of objects

Question

So I have data like this:

data = [
         [{a: "b", value: 12}, {a: "bb", value: 39}, {a: "bb", value: 150}],
         [{a: "c", value: 15}, {a: "cc", value: 83}, {a: "ccc", value: 12}],
         [{a: "d", value: 55}, {a: "dd", value: 9}, {a: "dd", value: 1}]
       ]

I want to get max values of value in each array of objects. So the result should be like this:

maxValues = [150, 83, 55]

Right now my code is:

let maxValues = []
let tmp;
let highest = Number.NEGATIVE_INFINITY;

data.map((eachArr, index) => {
  for(let i = eachArr.length -1; i >= 0; i--){
    tmp = eachArr[i].value;
    if(tmp > highest) highest = tmp;
  }
  maxValues.push(highest)
})

and the result is

maxValues = [150, 150, 150]

How can I achieve this?

Answer 1

You could use the spread syntax and take the max of mapped value.

The spread syntax allows an expression to be expanded in places where multiple arguments (for function calls) or multiple elements (for array literals) or multiple variables  (for destructuring assignment) are expected.

var data = [[{ a: "b", value: 12}, {a: "bb", value: 39 }, {a: "bb", value: 150 }], [{ a: "c", value: 15}, {a: "cc", value: 83 }, {a: "ccc", value: 12 }], [{ a: "d", value: 55}, {a: "dd", value: 9 }, {a: "dd", value: 1 }]],
    result = data.map(a => Math.max(...a.map(b => b.value)));

console.log(result);

Answer 2

You have to include let highest = Number.NEGATIVE_INFINITY; inside forEach function, because you have to set highest from every set in your array.

data = [
         [{a: "b", value: 12}, {a: "bb", value: 39}, {a: "bb", value: 150}],
         [{a: "c", value: 15}, {a: "cc", value: 83}, {a: "ccc", value: 12}],
         [{a: "d", value: 55}, {a: "dd", value: 9}, {a: "dd", value: 1}]
       ]
let maxValues = []
let tmp;
data.forEach((eachArr, index) => {
  let highest = Number.NEGATIVE_INFINITY;
  for(let i = eachArr.length -1; i >= 0; i--){
    tmp = eachArr[i].value;
    if(tmp > highest) highest = tmp;
  }
  maxValues.push(highest)
})
console.log(maxValues);

Answer 3

Ecmascript 5 solution with Math.max.apply() and Array.prototype.map() functions:

var data = [
    [{a: "b", value: 12}, {a: "bb", value: 39}, {a: "bb", value: 150}],
    [{a: "c", value: 15}, {a: "cc", value: 83}, {a: "ccc", value: 12}],
    [{a: "d", value: 55}, {a: "dd", value: 9}, {a: "dd", value: 1}]
];

var maxValues = data.map(function (arr) {
    return Math.max.apply(null, arr.map(function(o){ return o.value; }));
});

console.log(maxValues);

Math.max.apply() function will return the largest of the given numbers.
The numbers(value attribute of each nested object) are accumulated via Array.prototype.map() function.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/max