How to get the Index of Max/Min Values in JavaScript Arrays

Dealing with mood swings of Javascript arrays? In this blog post, you will understand how to find the Highs (global maximas) and Lows (global minimas) of JS array. Lets begin.

Getting Max Value(s)

Getting the first index using Math.max() and Array.indexOf()

const heights = [3, 5, 8, 100, 20];
const max = Math.max(...heights);
const index = heights.indexOf(max);

console.log(index); // 👉️ 3

Explanation:

• Utilize Math.max(...heights) to find the maximum value.
• Leverage Array.indexOf() to get the index of the maximum value.
• ⚠ Note: If multiple peaks share the same maximum value, indexOf returns only the index of the first occurrence.

Getting all the indices using loop and Math.max()

Employ a loop to iterate over the array and push indexes with the maximum value to the indexes array.

const heights = [3, 5, 8, 100, 20, 100];
const max = Math.max(...heights);
const indexes = [];

for (let i = 0; i < heights.length; i++) {
  if (heights[i] === max) {
    indexes.push(i);
  }
}

console.log(indexes); // 👉️ [3, 5]

Using Array.reduce()

Embrace Array.reduce() to iterate and find the index with the maximum value.

const heights = [3, 5, 8, 100, 20];
const index = heights.reduce((acc, cur, i) => (cur > heights[acc] ? i : acc), 0);

console.log(index); // 👉️ 3

Or use reduce to accumulate indexes with the maximum value in the indexes array. Now you get all such indices too.

const heights = [3, 5, 8, 100, 20];
const index = heights.reduce((acc, cur, i) => (cur > heights[acc] ? i : acc), 0);

console.log(index); // 👉️ 3

Getting MinValue(s)

Now that you know Max, almost exact code can be reused for minimas too.

Getting the first index using Math.min() and Array.indexOf()

const depths = [10, 5, 0, 15, 30];
const min = Math.min(...depths);
const index = depths.indexOf(min);

console.log(index); // 👉️ 2

Explanation:

• Utilize Math.min(...depths) to find the minimum value.
• Leverage Array.indexOf() to get the index of the minimum value.
• ⚠ Note: If multiple peaks share the same maximum value, indexOf returns only the index of the first occurrence.

Getting all the indices using loop and Math.min()

Employ a loop to iterate over the array and push indexes with the minimum value to the indexes array.

const depths = [10, 5, 0, 15, 30, 0, 0];
const min = Math.min(...depths);
const indexes = [];

for (let i = 0; i < depths.length; i++) {
  if (depths[i] === min) {
    indexes.push(i);
  }
}

console.log(indexes); // 👉️ [2, 5, 6]

Using Array.reduce()

Embrace Array.reduce() to iterate and find the index with the maximum value.

const depths = [10, 5, 0, 15, 30, 0, 0];
const index = heights.reduce((acc, cur, i) => (cur < depths[acc] ? i : acc), 0);

console.log(index); // 👉️ 2

Or use reduce to accumulate indexes with the minimum value in the indexes array. Now you get all such indices.

const depths = [10, 5, 0, 15, 30, 0, 0];
const min = Math.min(...depths);
const indexes = depths.reduce((acc, cur, i) => (cur === min ? [...acc, i] : acc), []);

console.log(indexes); // 👉️ [2, 5, 6]

🧪Practice Coding Problem: Local Peak Finder 🗻

In the spirit of Test Driven Development ( 😁), lets test our understanding by solving a problem.

You are given an array representing the heights of hills. Your task is to find the index or indices of the peak(s), which are the elements greater than their immediate neighbors. Note, these are not the absolute peaks of the whole array.

JavaScript

/**
 * Find the index or indices of the peak(s) in the given array.
 * @param {number[]} heights - Array representing the heights of hills.
 * @returns {number[]} - Array containing the index or indices of the peak(s).
 */
function findPeaks(heights) {
  // > > > 👉 Write code here 👈 < < <  
}

const hillHeights = [1, 3, 2, 5, 1, 4, 2];
console.log(findPeaks(hillHeights)); // 👉️ [3, 5]

function findPeaks(heights) {
  const peaks = [];

  for (let i = 1; i < heights.length - 1; i++) {
    if (heights[i] > heights[i - 1] && heights[i] > heights[i + 1]) {
      peaks.push(i);
    }
  }

  return peaks;
}

Now you know how scale the heights and dive the depths of a Javascript array.

Keep peaking and keep coding 🚀!