Finding max value in an array of sub arrays

Question

function largestOfFour(arr) {
  let newArr = [];
  let max = 0;
  for(let i = 0; i<arr.length;i++){
      for(let j = 0; j<arr[i].length; j++){
          if(arr[i][j]>max){
            max = arr[i][j];
            console.log(max);
            newArr.push(max);
          }
      }
      
  }
  return newArr;
}

Hello I am writing a code to find the max value in an array of sub arrays and am required to add that max value to a new array. My code is above. The problem is my code is pushing every value greater than the max to the new array. When I just want the true max without using the Math.max function. I believe this is happening because I do not have a way of updating the max when a new max is found. Some guidance would be very helpful

@NinaScholz hence why not an answer. Without max [[1,2,3],[5,6],[7]].map(a => a.reduce((max, n) => max > n ? max : n, a[0])) — epascarello
– epascarello, Commented Oct 19, 2020 at 17:04

Ori Drori · Accepted Answer · 2020-10-19 16:25:11Z

4

Initialize max in the outer loop (i) with -Infinity (the smallest "number" available"), then compare and update it in the inner loop, but only push it after the inner loop is done:

function largestOfFour(arr) {
  const newArr = [];
  for (let i = 0; i < arr.length; i++) {
    let max = -Infinity;
    for (let j = 0; j < arr[i].length; j++) {
      if (arr[i][j] > max) {
        max = arr[i][j];
      }
    }

    newArr.push(max);
  }
  return newArr;
}

const result = largestOfFour([[4, 3, 2, 1], [1, 2, 3, 4], [500, 600, 400], [300, 1000, 700]]);

console.log(result);

answered Oct 19, 2020 at 16:25

Ori Drori

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Comments

Nina Scholz · Accepted Answer · 2020-10-19 16:48:23Z

2

You could save the first value as start value for max and iterate from the second index.

Later push the max value of the nested array to the result array.

function largestOfFour(arrays) {
    const maxValues = [];
    for (let [max, ...array] of arrays) {
        for (const value of array) if (max < value) max = value;
        maxValues.push(max);
    }
    return maxValues;
}

console.log(largestOfFour([[3, 2, 1, 7], [2, 6, 4, 9], [2, 2, 1, 1], [4, 3, 6, 7]]));

edited Oct 19, 2020 at 16:48

answered Oct 19, 2020 at 16:28

Nina Scholz

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2 Comments

Ori Drori Over a year ago

Nice. You destructure in the for...of ([first, ...array]), and then you can convert the inner loop to for...of as well.

Behzad Hassani Over a year ago

pro answer LIKE

Aurora · Accepted Answer · 2020-10-19 16:37:34Z

0

From your description of the problem i can understand that you want the maximum value from the subarrays of the array. In this situation you do not need to use newArr.push(max) Inside the IF block. You can use this line after the two nested loop are finished. Then you use newArr.push(max); And then return newarr.

edited Oct 19, 2020 at 16:37

answered Oct 19, 2020 at 16:36

Aurora

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1 Comment

Behzad Hassani Over a year ago

Explain more with examples. he is new user

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