JavaScript重复元素处理方法分析【统计个数、计算、去重复等】

JavaScript重复元素处理方法分析【统计个数、计算、去重复等】

在JavaScript中，处理重复元素是常见的需求，本篇文章将分析几种处理重复元素的方法，包括统计个数、计算、去重复等。

统计个数

统计重复元素的个数是最常见的需求，以下是一些实现方法：

方法1：for循环+计数器

let arr = ["apple", "banana", "apple", "grape", "banana"];
let count = {};
for(let i = 0; i < arr.length; i++){
  if(!count[arr[i]]){
    count[arr[i]] = 1;
  }else{
    count[arr[i]]++;
  }
}
console.log(count); //{ apple: 2, banana: 2, grape: 1 }

方法2：foreach循环+计数器

let arr = ["apple", "banana", "apple", "grape", "banana"];
let count = {};
arr.forEach(function(item){
  if(!count[item]){
    count[item] = 1;
  }else{
    count[item]++;
  }
})
console.log(count); //{ apple: 2, banana: 2, grape: 1 }

方法3：reduce方法

let arr = ["apple", "banana", "apple", "grape", "banana"];
let count = arr.reduce(function(pre, cur){
  pre[cur] ? pre[cur]++ : pre[cur] = 1;
  return pre;
}, {});
console.log(count); //{ apple: 2, banana: 2, grape: 1 }

计算

计算重复元素的总和、平均值等情况也是常见的需求，以下是一些实现方法：

方法1：for循环+计数器+计算器

let arr = [1, 3, 5, 5, 7, 9, 9];
let count = 0;
let sum = 0;
for(let i = 0; i < arr.length; i++){
  count++;
  sum += arr[i];
}
let avg = sum/count;
console.log(avg) //5.571428571428571

方法2：foreach循环+计数器+计算器

let arr = [1, 3, 5, 5, 7, 9, 9];
let count = 0;
let sum = 0;
arr.forEach(function(item){
  count++;
  sum += item;
})
let avg = sum/count;
console.log(avg) //5.571428571428571

方法3：reduce方法

let arr = [1, 3, 5, 5, 7, 9, 9];
let count = arr.length;
let sum = arr.reduce(function(pre, cur){
  return pre + cur;
}, 0);
let avg = sum/count;
console.log(avg) //5.571428571428571

去重复

去重复也是常见的需求，以下是一些实现方法：

方法1：for循环+indexOf+新数组

let arr = ["apple", "banana", "apple", "grape", "banana"];
let newArr = [];
for(let i = 0; i < arr.length; i++){
  if(newArr.indexOf(arr[i]) == -1){
    newArr.push(arr[i]);
  }
}
console.log(newArr); //["apple", "banana", "grape"]

方法2：forEach循环+includes+新数组

let arr = ["apple", "banana", "apple", "grape", "banana"];
let newArr = [];
arr.forEach(function(item){
  if(!newArr.includes(item)){
    newArr.push(item);
  }
})
console.log(newArr); //["apple", "banana", "grape"]

方法3：Set数据结构

let arr = ["apple", "banana", "apple", "grape", "banana"];
let newArr = [...new Set(arr)];
console.log(newArr); //["apple", "banana", "grape"]

总结

以上是JavaScript中处理重复元素的一些实现方法，其中统计个数、计算和去重复都是常见的需求，选择哪种方法主要取决于具体场合和需求。