数组里计算元素查询次数

方法一

  var _res = []

            this.a.sort()

            for (var i = 0; i < this.a.length;) {

               var count = 0

               for (var j = i; j < this.a.length; j++) {

                if (this.a[i] === this.a[j]) {

                   count++

                }

               }

               _res.push([this.a[i], count])

               console.log(_res)

            }

//统计一个数组中有多少个不重复的单词：
// 不用reduce时：

方法二
var arr = ["apple", "orange", "apple", "orange", "pear", "orange"];

// function getWordCnt() {
var obj = {};
for (var i = 0, l = arr.length; i < l; i++) {
var item = arr[i];
obj[item] = (obj[item] + 1) || 1;
}
console.log(Object.keys(obj))
// return obj;
// }
console.log(getWordCnt())
// 用reduce时：

方法三
var arr = ["apple", "orange", "apple", "orange", "pear", "orange"];

function getWordCnt() {
return arr.reduce(function(prev, next) {
prev[next] = (prev[next] + 1) || 1;
return prev;
}, {});
}
console.log(getWordCnt()); //{apple: 2, orange: 3, pear: 1}