js计算数组中某个元素重复出现的个数

文章转载自https://blog.csdn.net/lixiaoyan93/article/details/88719333

1、计算特定值的重复个数

let counts = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0);
 
console.log('数组counts中"李"出现的次数是：'+counts(["李","李","设","弟","弟","生","生","李"],"李"));

结果：数组counts中"李"出现的次数是：3

2、计算数组中每个元素的重复个数

// 不用reduce时：
var arr = ["李","李","设","弟","弟","生","生","李"]; 
function getRepeatNum(){ 
    var obj = {}; 
    for(var i= 0, l = arr.length; i< l; i++){ 
        var item = arr[i]; 
        obj[item] = (obj[item] +1 ) || 1; 
    } 
    return obj; 
}
console.log(getRepeatNum());

结果：{李: 3, 设: 1, 弟: 2, 生: 2}

// 用reduce时：
var arr = ["李","李","设","弟","弟","生","生","李"]; 
function getRepeatNum(){ 
    return arr.reduce(function(prev,next){ 
        prev[next] = (prev[next] + 1) || 1; 
        return prev; 
    },{}); 
} 
console.log(getRepeatNum());

结果：{李: 3, 设: 1, 弟: 2, 生: 2}