如何在数组数组中的相同索引处获取最大值？

Question

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 the largest value at the same index in this data, so I want the result to be like this:

[55, 83, 150]

Right now, I can get each value in objects, and I can get the largest value if I specify the index. I am not sure how to do it with every index.

let array = [];
data.map((eachArr, index) => {
   array.push(eachArr[0].value)

   for(let i = 0; i < eachArr.length; i++){
     console.log('eachArr[i].value', eachArr[i].value, i);
   }
})
console.log(Math.max(...array)) ===> 55

How can I do this?

I think people misunderstood my question. I do not want the largest value from each array. I want the largest value of value with the same index in every array. So I want 55 from 12, 15, 55, 83 from 39, 83, 9, and 150 from 150, 12, 1. I am sorry for not being specific. I should have an example with different length.

Answer 1

Use Array#reduce method with Array#forEach method.

 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 }]]; console.log( // iterate over the array data.reduce(function(arr, ele) { // iterate over the inner array ele.forEach(function(o, i) { // check element present at the index, if not then update with current value arr[i] = arr[i] || o.value; // check assign greatest value by comparing with previous value arr[i] = arr[i] < o.value ? o.value : arr[i]; // you can combine above two lines // arr[i] = !arr[i] || arr[i] < o.value ? o.value : arr[i]; }); // return the array reference return arr; // set initial value as an empty array }, []) ) // without any comments console.log( data.reduce(function(arr, ele) { ele.forEach(function(o, i) { arr[i] = !arr[i] || arr[i] < o.value ? o.value : arr[i]; }); return arr; }, []) ) 

---

With ES6 arrow function :

 let 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 }]]; console.log( data.reduce((arr, ele) => (ele.forEach((o, i) => arr[i] = !arr[i] || arr[i] < o.value ? o.value : arr[i]), arr), []) ) 

---

Using the simple for loop with the same logic.

 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 res = []; for (var i = 0; i < data.length; i++) { for (var j = 0; j < data[i].length; j++) { res[j] = !res[j] || res[j] < data[i][j].value ? data[i][j].value : res[j]; } } console.log(res); 

---

FYI : Performance comparison

Answer 2

This should do it.

// Get the maxes from rows
 data.map(function(a){
    return Math.max.apply( null, a.map(function(b){ return b.value; }) );
 });

// Get maxes from cols
var maxes = data.map(function(v,i){
    return Math.max.apply( null, data.map(function(a){
       return a[i].value;
    }));
});
console.log("Maxes: ",maxes);
// Maxes:  [ 55, 83, 150 ]

Answer 3

In ES6:

 const data = [ [{a: "b", value: 12}, {a: "bb", value: 39}, {a: "bb", value: 11}], [{a: "c", value: 15}, {a: "cc", value: 83}, {a: "cc", value: 12}], [{a: "d", value: 55}, {a: "dd", value: 9}, {a: "dd", value: 1}] ]; const result = data[0].map((_, i) => Math.max(...data.map(subarray => subarray[i].value))); console.log(result); 

Note that this will not work properly if the subarrays are not of the same length.

If you prefer an ES5 version:

const result = data[0].map(function(_, i) {
  return Math.max.apply(null, data.map(function(subarray) {
    return subarray[i].value;
  }));
});