javascript - Search An Array Consisting of Sub-Arrays For the Largest Number and Return in a New Array

Question

I am working on a coding challenge to take a given array which consists of sub-arrays, search for the largest number in each sub-array, and finally return a new array consisting only of the largest numbers. My thought process was to create variables out of each subarray, write a for-loop comparing each value within the array, then push the largest value to a new array. After writing my first for-loop I tested my code and see that I am getting an unexpected result of the entire first subarray being pushed into my new array. I am looking for the mistake before I write the next three loops. Thank you. Edit: This is for beginner JavaScript coders and the suggestion indicates to use comparison operators in your solution.

function largestOfFour(arr) {
      var one = arr[0];
      var two = arr[1];
      var three = arr[2];
      var four = arr[3];
      var newArr = [];

      for (var i = 0; i < one.length; i++){
        var oneLrg = 0;
        if (one[i] > oneLrg){
          oneLrg = one[i];
          }
        newArr.push(oneLrg);
      }  

  return arr;
}

console.log(largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]])); //This test case returns [4,5,1,3] instead of just [5]

Answer 1

Using >:

var newArr = [];
for(var i=0; i<arr.length; ++i) {           // Iterate array
  var maximum = -Infinity;                  // Initial maximum
  for(var j=0; j<arr[i].length; ++j)        // Iterate subarrays
    if(arr[i][j] > maximum)                 // Compare
      maximum = arr[i][j];                  // Update maximum
  newArr.push(maximum);                     // Store the real maximum
}

Using Math.max:

var newArr = [];
for(var i=0; i<arr.length; ++i) {           // Iterate array
  var maximum = -Infinity;                  // Initial maximum
  for(var j=0; j<arr[i].length; ++j)        // Iterate subarrays
    maximum = Math.max(maximum, arr[i][j]); // Update maximum
  newArr.push(maximum);                     // Store the real maximum
}

Adding apply:

var newArr = [];
for(var i=0; i<arr.length; ++i)     // Iterate array
  newArr.push(                      // Store ...
    Math.max.apply(Math, arr[i])    // ... the maximum of the subarray
  );

Adding ECMAScript 5 map,

var newArr = arr.map(function(subarray) {
  return Math.max.apply(Math, subarray);
});

Adding ECMAScript 5 bind,

var newArr = arr.map(Function.apply.bind(Math.max, Math));

Or adding ECMAScript 6 arrow functions and spread operator,

var newArr = arr.map(subarray => Math.max(...subarray));