比较对象数组中的属性值

Question

so i'm doing some excercises as practice, since i'm a beginner, and i stumble into this problem that i can't solve, would anybody be kind to give me a hand?

i would like to make a function that returns how many people is 18 or older, this is what i've been trying but i'm a bit confused..

const examplePeople = [
  { name: 'John', age: 15 },
  { name: 'Jane', age: 16 },
  { name: 'Jack', age: 25 },
  { name: 'Ana', age: 18 },
  { name: 'Raul', age: 23 },
  { name: 'Pedro', age: 17 }
];

function countLegalPeople(people) {
  for (i= 0; i >= people["age"] ; i++){
    if (people[i]["age"] >= 18) {
      return people[i];
    }
  }
}

console.log(countLegalPeople(examplePeople));

Answer 1

I'd use reduce , where the accumulator is the number of objects found so far that pass the test:

 const examplePeople = [ { name: 'John', age: 15 }, { name: 'Jane', age: 16 }, { name: 'Jack', age: 25 }, { name: 'Ana', age: 18 }, { name: 'Raul', age: 23 }, { name: 'Pedro', age: 17 } ]; const result = examplePeople.reduce((a, { age }) => a + (age >= 18), 0); console.log(result); 

With a for loop, you'd have to increment a more persistent variable, eg

 const examplePeople = [ { name: 'John', age: 15 }, { name: 'Jane', age: 16 }, { name: 'Jack', age: 25 }, { name: 'Ana', age: 18 }, { name: 'Raul', age: 23 }, { name: 'Pedro', age: 17 } ]; let result = 0; for (let i = 0; i < examplePeople.length; i++) { if (examplePeople[i].age >= 18) { result++; } } console.log(result); 

But array methods are generally more terse and elegant IMO.

Answer 2

Why don't try Array.prototype.filter()

 const examplePeople = [ { name: 'John', age: 15 }, { name: 'Jane', age: 16 }, { name: 'Jack', age: 25 }, { name: 'Ana', age: 18 }, { name: 'Raul', age: 23 }, { name: 'Pedro', age: 17 } ]; function countLegalPeople(people) { return people.filter(p => p.age >= 18).length; } console.log(countLegalPeople(examplePeople)); 

Answer 3

The issue with your approach is that you are returning within your for loop. Whenever you return, your function will stop running (it essentially jumps out of your function), so, whenever you run into a person over the age of 18 you stop your loop and thus it cannot count any more people.

Instead, you can create a variable and set it to zero. This will count how many people of the age of 18 you have seen. To do this, you will need to add one to this variable each time you see a person of an age of 18 or higher. Then, once your for loop is complete, you can return this number.

See example below:

 const examplePeople = [ { name: 'John', age: 15 }, { name: 'Jane', age: 16 }, { name: 'Jack', age: 25 }, { name: 'Ana', age: 18 }, { name: 'Raul', age: 23 }, { name: 'Pedro', age: 17 } ]; function countLegalPeople(people) { let counter = 0; // number of people >= 18; for (let i= 0; i < people.length; i++){ // loop through the array of people (using people.length) if (people[i]["age"] >= 18) { counter++; // age 1 to counter (same as counter = counter + 1) } } return counter; // return the amount of people >= 18 } console.log(countLegalPeople(examplePeople)); 

Answer 4

Your question was slightly confusing and could be taken two different ways, so if you are looking to return the total instances of people that are 18 and older in a new array, you would do something like this:

const examplePeople = [
  { name: 'John', age: 15 },
  { name: 'Jane', age: 16 },
  { name: 'Jack', age: 25 },
  { name: 'Ana', age: 18 },
  { name: 'Raul', age: 23 },
  { name: 'Pedro', age: 17 }
];

let adults = [];
for (let i = 0; i < examplePeople.length; i++) {
  if (examplePeople[i].age >= 18) {
    adults.push(examplePeople[i]);
  }
}
console.log(adults);

you can also get the length with a simple:

console.log(adults.length);