Lodash：将具有重复值的数组转换为具有重复出现次数的对象

Question

这是我的数组：

['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California']

lodash 中是否有办法将其转换为具有重复出现次数的对象，如下所示：

[
    {'name':'California', 'count':2},
    {'name':'Texas', 'count':3},
    {'name':'New York', 'count':1},
    {'name':'Missouri', 'count':1},
    {'name':'New Mexico', 'count':1},
]

我尝试了很多组合，但都没有成功。文档：https://lodash.com/docs#countBy

Answer 1

你可以只映射_.countBy的结果。

var array = ['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California'],
    count = _.countBy(array),
    result = _.map(count, (v, k) => ({ name: k, count: v }));

console.log(count);
console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.15.0/lodash.min.js"></script>

结合_.chain

var array = ['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California'],
    count = _
        .chain(array)
        .countBy()
        .map((v, k) => ({ name: k, count: v }));

console.log(count);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.15.0/lodash.min.js"></script>

Answer 2

您可以通过reduce() 做到这一点

var ar = ['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California'];

var obj = {}
var result = ar.reduce(function(r, e) {
  if(!obj[e]) {
    obj[e] = {name: e, count: 0};
    r.push(obj[e])
  }
  obj[e].count++;
  return r;
}, [])

console.log(result)

Answer 3

我不确定是否有内置函数可以实现，但您可以使用标准方法来实现。

var arr = ['California', 'Texas', 'Texas', 'Texas', 'New York', 'Missouri', 'New Mexico', 'California'];
var obj = [];

arr.forEach(a => {
    var b = obj.find(b => b.name == a);
    if(!b){
        obj.push({
            name: a,
            count: 1
        });
    }else{
        b.count++;
    }
});

console.log(JSON.stringify(obj, null, 2));

Answer 4

正如你所说，有 countBy 函数，你必须映射结果以根据需要设置格式：

var result = _( array )
  .countBy( )
  .map( ( key, value ) => ( { name: key, count: value } ) )
  .value( )

console.log( result );

Answer 5

两行纯 JS。

var arr = ['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California'],
    lut = arr.reduce((p,c) => p[c] ? (p[c]++ ,p) : (p[c] = 1, p),{});
 result = Object.keys(lut).map(k => ({name:k,count:lut[k]}));
console.log(result);

Answer 6

在纯 Javascript 中，您可以使用 Array#forEach。

var data = ['toString', 'California', 'Texas', 'Texas', 'Texas', 'New York', 'Missouri', 'New Mexico', 'California'],
    count = [];

data.forEach(function (a) {
    if (!this[a]) {
        this[a] = { name: a, count: 0 };
        count.push(this[a]);
    }
    this[a].count++;
}, Object.create(null));

console.log(count)

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带有{}的版本

var data = ['toString', 'California', 'Texas', 'Texas', 'Texas', 'New York', 'Missouri', 'New Mexico', 'California'],
    count = [];

data.forEach(function (a) {
    if (!this[a]) {
        this[a] = { name: a, count: 0 };
        count.push(this[a]);
    }
    this[a].count++;
}, {}); // no Object.create(null)!

console.log(count)

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