查找数组(字符串)中值出现的次数

统计一个数组或者一个字符串中每个值出现的次数

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常规for循环

var egFor = function(strArr){    const chars = {};    for(let i=0;i<strArr.length;i++){        const ch = strArr[i];        if(!chars[ch]){            chars[ch] = 0;        }        chars[ch]++;        // chars[ch] = (chars[ch] +1 ) || 1;    }    return chars;}console.log(egFor('abababababaababba'));//{a: 9, b: 8}console.log(egFor([1,2,3,4,5,6,7,3,32,2,21,2]));//{1: 1, 2: 3, 3: 2, 4: 1, 5: 1, 6: 1, 7: 1, 21: 1, 32: 1}

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reduce()方法 不能用于字符串 可以将字符串转为数组在使用reduce()方法

var egReduce = function(strArr){    const arrStr = strArr;    return arrStr.reduce(function(prev,next){        // console.log("prev:",prev);        // console.log("next:",next);        prev[next] = (prev[next]+1) || 1;        return prev;  },{});}console.log(egReduce([1,2,3,4,5,6,7,3,32,2,21,2]));//{1: 1, 2: 3, 3: 2, 4: 1, 5: 1, 6: 1, 7: 1, 21: 1, 32: 1}