JavaScript：在对象数组中循环并使用reduce函数查找特定键的总和

Question

I have the following object below. It contains an array of objects. Each object is a superhero that contains details about the superhero.

const superheroes = [
      {
        name: 'Bruce Wayne',
        alias: 'Batman',
        powerLevel: 50,
        universe: 'DC Comics',
        race: 'Human',
      },
      {
        name: 'Wade Wilson',
        alias: 'Deadpool',
        powerLevel: 90,
        universe: 'Marvel Comics',
        race: 'Mutant',
      },
      {
        name: 'Peter Parker',
        alias: 'Spiderman',
        powerLevel: 70,
        universe: 'Marvel Comics',
        race: 'Human',
      },
      {
        name: 'Kristin Wells',
        alias: 'Superwoman',
        powerLevel: 99,
        universe: 'DC Comics',
        race: 'Kryptonian',
      },
      {
        name: 'Barry Allen',
        alias: 'The Flash',
        powerLevel: 80,
        universe: 'DC Comics',
        race: 'Human',
      },
      {
        name: 'Diana Prince',
        alias: 'Wonder Woman',
        powerLevel: 90,
        universe: 'DC Comics',
        race: 'Human',
      },
      {
        name: 'Ororo Munroe',
        alias: 'Storm',
        powerLevel: 85,
        universe: 'Marvel Comics',
        race: 'Mutant',
      },
      {
        name: 'Helen Parr',
        alias: 'Elastigirl',
        powerLevel: 70,
        universe: 'Dark Horse Comics',
        race: 'Human',
      },
    ];

I want to find the average power level of all the superheroes.

I tried the code below:

function powerLevelAverage(obj){

  let sum = 0; 
  let objCount = 0;

  return obj.reduce((accumulator, element) => {

    objCount += 1; 
    console.log(objCount)

    sum = accumulator + element.powerLevel

    return sum; 

  }, 0)
  return Math.round(sum/objCount); 
}


const averagePowerLevel = powerLevelAverage(superheroes);

averagePowerLevel

The code appears to return the sum of 634 but does not return the average. What am I doing wrong?

Note: I want to use reduce modifying function to solve this problem.

Answer 1

There are three mistakes:

• You have two return statements in the code. So the code will not reach to the second one which gets average.
• You are using reduce() in a wrong way. You are not using accumulator anywhere. You are using reduce() like forEach()
• You don't need to count each object in reduce() you already have the length of array in form of obj.length

A cleaner code can be.

function powerLevelAverage(obj){
  return Math.round(obj.reduce((ac,a) => ac + a.powerLevel,0)/obj.length)
}

Working snippet:

 const superheroes = [ { name: 'Bruce Wayne', alias: 'Batman', powerLevel: 50, universe: 'DC Comics', race: 'Human', }, { name: 'Wade Wilson', alias: 'Deadpool', powerLevel: 90, universe: 'Marvel Comics', race: 'Mutant', }, { name: 'Peter Parker', alias: 'Spiderman', powerLevel: 70, universe: 'Marvel Comics', race: 'Human', }, { name: 'Kristin Wells', alias: 'Superwoman', powerLevel: 99, universe: 'DC Comics', race: 'Kryptonian', }, { name: 'Barry Allen', alias: 'The Flash', powerLevel: 80, universe: 'DC Comics', race: 'Human', }, { name: 'Diana Prince', alias: 'Wonder Woman', powerLevel: 90, universe: 'DC Comics', race: 'Human', }, { name: 'Ororo Munroe', alias: 'Storm', powerLevel: 85, universe: 'Marvel Comics', race: 'Mutant', }, { name: 'Helen Parr', alias: 'Elastigirl', powerLevel: 70, universe: 'Dark Horse Comics', race: 'Human', }, ]; function powerLevelAverage(obj){ return Math.round(obj.reduce((ac,a) => ac + a.powerLevel,0)/obj.length) } console.log(powerLevelAverage(superheroes)) 

Answer 2

You're returning your sum right here, which doesn't account for your division....

Change this to

function powerLevelAverage(obj){

  let sum = 0; 
  let objCount = 0;

  return obj.reduce((accumulator, element) => {

    objCount += 1; 
    console.log(objCount)

    sum = accumulator + element.powerLevel

    // return sum; // Just get rid of this

  }, 0)
  return Math.round(sum/objCount); 
}