9. 유용한 10가지 배열 함수들. Array APIs 총정리

** 이 글은 유튜브 강의을 보고 공부하면서 스스로 콘솔로 작성하고, 따라치면서 Javascript 기초 공부를 하는 공간입니다.

 

www.youtube.com/watch?v=3CUjtKJ7PJg&list=PLv2d7VI9OotTVOL4QmPfvJWPJvkmv6h-2&index=9

// Q1. make a string out of an array (틀림ㅜㅜㅜㅜ)
{
  const fruits = ['apple', 'banana', 'orange'];
  
  const result = fruits.join('|');
  const result2 = fruits.join();

  console.log(result); //"apple|banana|orange"
  console.log(result2); //"apple,banana,orange"


}

// Q2. make an array out of a string(틀림ㅜㅜㅜㅜ)
{
  const fruits = '🍎, 🥝, 🍌, 🍒';
   const result = fruits.split(',');
    console.log(result); //["🍎"," 🥝"," 🍌"," 🍒"]


}

// Q3. make this array look like this: [5, 4, 3, 2, 1]
{
  const array = [1, 2, 3, 4, 5];
  const newArray = [];
  for(let a = array.length -1 ; a >= 0; a--){
    newArray.push(array[a]);
  }
  
 console.log(newArray, "Q3");

// 해결방법
 const result = array.reverse(); //array 배열자체도 reverse 하게 되어진다!
 console.log(result); // [5, 4, 3, 2, 1]
   console.log(array); // [5, 4, 3, 2, 1]

}

// Q4. make new array without the first two elements
{
  const array = [1, 2, 3, 4, 5];
  
  array.shift();
  array.shift();
  
 // console.log(array, "Q4"); 

  // 해결방법
const result = array.slice(2,5);
  console.log(result); //[3,4,5]
  console.log(array); //[1, 2, 3, 4, 5]
  
}

class Student {
  constructor(name, age, enrolled, score) {
    this.name = name;
    this.age = age;
    this.enrolled = enrolled;
    this.score = score;
  }
}
const students = [
  new Student('A', 29, true, 45),
  new Student('B', 28, false, 80),
  new Student('C', 30, true, 90),
  new Student('D', 40, false, 66),
  new Student('E', 18, true, 88),
];

// Q5. find a student with the score 90
{

  for( value of students ){
    if(value['score'] == '90'){
     //     console.log(value['name'], "Q5");
    }
  }
  
    // 해결방법
const result = students.find((student) => student.score == 90);  
console.log(result);
  
}

// Q6. make an array of enrolled students
{
  const arry6 =[];
  
  for(value of students){
    if(value['enrolled']){
      arry6.push(value);
    }
  }
  
 // console.log(arry6, "Q6");
      // 해결방법

  const result = students.filter((student) => student.enrolled);
  console.log(result);
  
}

// Q7. make an array containing only the students' scores
// result should be: [45, 80, 90, 66, 88]
{
  const arr7 = [];
  
  for(let i = 0; i < students.length ; i++ ){
    arr7.push(students[i]['score']);
  }
  
 //   console.log(arr7, "Q7");
  
      // 해결방법

  // 다른 방식의 데이터로 바꾸는것 ! 
  const result = students.map((student) => student.score);
  console.log(result);
  
}

// Q8. check if there is a student with the score lower than 50
{
    const arr8 = [];
  
  for(let i = 0; i < students.length ; i++ ){
    if(students[i]['score'] <= 50 ){
   //       console.log(students[i]['name'], "Q8");
    }
  }
        // 해결방법

  const result = students.some((student) => student.score < 50 ); // 있는지 없는지 확인하는것 
  console.log(result); // true
  
  const result2 = students.every((student) => student.score < 50 ); // 모든 배열이 충족되었는지 확인하는것
  console.log(result2); // false
  
  
}

// Q9. compute students' average score
{
  let average = 0;
  
    for(let i = 0; i < students.length ; i++ ){
    average += students[i]['score'];
      
  }
  
  //console.log(average / students.length , "Q9");
  
          // 해결방법

  const result = students.reduce((prev, curr) => {
    console.log('---------');
    console.log(prev);
    console.log(curr);

    return prev + curr.score;
  }, 0);
  
  console.log(result / students.length); //73.8
  
}

// Q10. make a string containing all the scores
// result should be: '45, 80, 90, 66, 88'
{
  const result = students.map((student) => student.score).join();
  console.log(result); //'45, 80, 90, 66, 88'
  
  const result1 = students
  .map((student) => student.score)
  .filter((student) => student >= 50)
  .join();
  
  console.log(result1); // 80, 90, 66, 88'
  
}

// Bonus! do Q10 sorted in ascending order
// result should be: '45, 66, 80, 88, 90'
{
    const result = students
    .map((student) => student.score)
    .sort((a,b) => a - b ) 
    .join()
    ;
    
    console.log(result); //'45, 66, 80, 88, 90'

    
  

}