How to count the number of identical numbers in an array using a function?

• 0
  You need to calculate using a function that receives an array and a specific number, the number of this specific number in the array of numbers.

  JavaScript Anonymous, Sep 27, 2019

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3 Answers
• 0

  const count = (arr, val) => arr.filter(n => n === val).length;
  
  // или
  
  const count = (arr, val) => arr.reduce((acc, n) => acc + (n === val), 0);

  
  
  It is possible and in a more general form, we consider everything:
  
  
  
  

  const count = arr => arr.reduce((acc, n) => acc.set(n, (acc.get(n) || 0) + 1), new Map);
  
  
  
  const arr = [ 1, 1, 1, 2, 2, 9, 9, 9, 9, 7, 'hello, world!!', 'hello, world!!' ];
  
  const counted = count(arr);
  
  console.log(counted.get(1)); // 3
  
  console.log(counted.get(9)); // 4
  
  console.log(counted.get('hello, world!!')); // 2

  
  
  UPD. In the comments, it was suggested that it would be nice to do something with the values ​​that were not represented in the original data. Let's substitute 0:
  
  
  
  

  function Counter(data, key = x => x) {
  
    const counted = new Map;
  
    for (const n of data) {
  
      const k = key(n);
  
      counted.set(k, (counted.get(k) || 0) + 1);
  
    }
  
  
  
    return k => counted.get(k) || 0;
  
  }

  
  
  You can use it like this:
  
  
  
  

  const arr = [ 1, 1, 1, 2, 2, 9, 9, 9, 9, 7, 'hello, world!!', 'hello, world!!' ];
  
  const counted = Counter(arr);
  
  console.log(counted(1)); // 3
  
  console.log(counted(10)); // 0

  
  
  Or like this:
  
  
  
  

  <span class="color">red</span>
  
  <span class="color">green</span>
  
  <span class="color">red</span>
  
  <span class="color">red</span>

  
  
  

  const counted = Counter(document.querySelectorAll('.color'), el => el.innerText);
  
  console.log(counted('red')); // 3
  
  console.log(counted('blue')); // 0

  Anonymous

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• 0

  nums.reduce((acc, n) => n === numToFind ? acc + 1 : acc, 0);

  Anonymous

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• 0

  function countValueInArray(yourArrName, inputValue) {
  
     return arr.reduce((count, item) => count + (item === inputValue), 0)
  
  };

  Anonymous

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