如何计算数组中每个项目的出现次数？ [英] How to count the number of occurrences of each item in an array?

问题描述

我有一个数组如下，

var arr = ['ab','pq','mn','ab','mn','ab']

预期结果

arr['ab'] = 3
arr['pq'] = 1
arr['mn'] = 2

尝试如下，

$.each(arr, function (index, value) {
    if (value) 
        arr[value] = (resultSummary[value]) ? arr[value] + 1 : 1;
});

console.log(arr.join(','));

推荐答案

无需使用jQuery执行此任务—这个例子将构建一个对象，其中包含数组中每个不同元素的出现量 O（n）

no need to use jQuery for this task — this example will build an object with the amount of occurencies of every different element in the array in O(n)

var occurrences = { };
for (var i = 0, j = arr.length; i < j; i++) {
   occurrences[arr[i]] = (occurrences[arr[i]] || 0) + 1;
}

console.log(occurrences);        // {ab: 3, pq: 1, mn: 2}
console.log(occurrences['mn']);  // 2

示例小提琴

---

您还可以使用 Array.reduce 获得相同的结果并避免 for-loop

---

You could also use Array.reduce to obtain the same result and avoid a for-loop

var occurrences = arr.reduce(function(obj, item) {
  obj[item] = (obj[item] || 0) + 1;
  return obj;
}, {});

console.log(occurrences);        // {ab: 3, pq: 1, mn: 2}
console.log(occurrences['mn']);  // 2

示例小提琴

这篇关于如何计算数组中每个项目的出现次数？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！