Question

我有这种类型的对象

students = [
    {
        "name": "Ana Barbique",
        "category":"B"
    }
    {
        "name": "Marko Polo",
        "category":"B"
    }
    {
        "name": "Nick Harper",
        "category":"A"
    }
]

我希望它拥有这种类型的对象数组：

sum = [
    {
        "category": "A",
        "count" : 1
    }
    {
        "category": "B",
        "count" : 2
    }
]

所以基本上我想让对象数组具有出现在学生中的类别及其数量。订单无关紧要。我以前没有这样做过。

Answer 1

首先通过减少students数组

来创建类别计数对象

const categories = students
   .reduce((cat, student) => (
       cat[student.category]++ || (cat[student.category] = 1), cat
   ), {})

然后迭代类别＆＃39;用于创建所需数组的键

const sum = Object
   .keys(categories)
   .map(name => ({category: name, count: categories[name]}))

Answer 2

这是一个纯粹的循环＆amp;查找方法。 Yuri Tarabanko的答案很简单。

这种方法的关键是使用check数组对象来保存sum []数组中每个类别的索引。这是一种有用的技术。

var students = [
    {
        "name": "Ana Barbique",
        "category":"B"
    },
    {
        "name": "Marko Polo",
        "category":"B"
    },
    {
        "name": "Nick Harper",
        "category":"A"
    }
]

var sum = [], check = [], obj;
for (var i = 0; i < students.length; i = i + 1) {

  obj = students[i]; 
  if ( check[obj.category] !== undefined ) { 
    // object has already been seen so add to sum array count
    sum[check[obj.category]].count = sum[check[obj.category]].count + 1; 
    
  }
   else {
   // object has not been seen so insert new.
   sum.push({"category": obj.category, "count": 1});
   check[obj.category] = sum.length - 1; // note index of category in sum array.   
   }


}
console.log('sum = ' + JSON.stringify(sum));

以这种方式对频率的对象阵列进行排序

2 个答案: