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JavaScript: Get the maximum value of an array, after mapping each element to a value using the provided function

JavaScript fundamental (ES6 Syntax): Exercise-86 with Solution

Write a JavaScript program to get the maximum value of an array, after mapping each element to a value using the provided function.

  • Use Array.prototype.map() to map each element to the value returned by fn.
  • Use Math.max() to get the maximum value.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const maxBy = (arr, fn) => Math.max(...arr.map(typeof fn === 'function' ? fn : val => val[fn]));
console.log(maxBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n));
console.log(maxBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'));

Sample Output:

8
8

Pictorial Presentation:

JavaScript Fundamental: Get the maximum value of an array, after mapping each element to a value using the provided function

Flowchart:

flowchart: Get the maximum value of an array, after mapping each element to a value using the provided function

Live Demo:

See the Pen javascript-basic-exercise-86-1 by w3resource (@w3resource) on CodePen.


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Previous: Write a JavaScript program to replace all but the last number of characters with the specified mask character.
Next: Write a JavaScript program to get the n maximum elements from the provided array. If n is greater than or equal to the provided array's length, then return the original array(sorted in descending order).

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JavaScript: Tips of the Day

How to remove a specific item from an array?

Find the index of the array element you want to remove using indexOf, and then remove that index with splice.

The splice() method changes the contents of an array by removing existing elements and/or adding new elements.

const array = [2, 5, 9];

console.log(array);

const index = array.indexOf(5);
if (index > -1) {
  array.splice(index, 1);
}

// array = [2, 9]
console.log(array);

The second parameter of splice is the number of elements to remove. Note that splice modifies the array in place and returns a new array containing the elements that have been removed.

For the reason of completeness, here are functions. The first function removes only a single occurrence (i.e. removing the first match of 5 from [2,5,9,1,5,8,5]), while the second function removes all occurrences:

function removeItemOnce(arr, value) {
  var index = arr.indexOf(value);
  if (index > -1) {
    arr.splice(index, 1);
  }
  return arr;
}

function removeItemAll(arr, value) {
  var i = 0;
  while (i < arr.length) {
    if (arr[i] === value) {
      arr.splice(i, 1);
    } else {
      ++i;
    }
  }
  return arr;
}
//Usage
console.log(removeItemOnce([2,5,9,1,5,8,5], 5))
console.log(removeItemAll([2,5,9,1,5,8,5], 5))

Ref: https://bit.ly/2N9nKRp