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Accepted
Данис Хамидуллин
Asked:2020-08-14 21:38:30 +0000 UTC2020-08-14 21:38:30 +0000 UTC

如何获取数组中某个值的出现次数

  • 772

该算法计算数组中元素的出现次数

var numbers = [2, 4, 4, 7, 6, 8, 4];

function howMany(array, value) {
    var n = 0;
    for (var i = 0; i < array.length; i++)
        if (array[i] == value)
            n++;
    return n;
}

console.log(howMany(numbers, 3)); // -> 0
console.log(howMany(numbers, 4)); // -> 3
console.log(howMany(numbers, 5)); // -> 0
console.log(howMany(numbers, 6)); // -> 0

数组应该有对应的方法吗？

javascript

3 个回答

  1. 您可以使用闭包来保存第一次遍历数组的结果并重用它们。

    function howMany(arr) {
  const map = arr.reduce((c, item) => (c[item]=(c[item]||0) + 1, c), {});
  
  return num => map[num];
}

const data = [1, 5, 4, 3, 4, 6, 4, 7, 1];

console.log(howMany(data)(4)); // 3

const howManyInData = howMany(data);
console.log(howManyInData(1), howManyInData(4)); // 2 3

    • 1 

  2. const numbers = [2, 4, 4, 7, 6, 8, 4];

Array.prototype.howMany = function(value) {
    return this.reduce((prev, curr) => {
      return curr === value ? prev+1 : prev
    }, 0);
}

console.log(numbers.howMany(3));
console.log(numbers.howMany(4));
console.log(numbers.howMany(5));
console.log(numbers.howMany(6));

    • 0
  3. Best Answer

    评论中free_ze的回答解决了这个问题

    array.filter(x => x === value).length
    • 0

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