javascript计数键值对

Question

我想遍历一个对象数组，并根据像哈希表这样的特定属性值类型返回另一个具有记录数的对象数组。

例如：

Array1 = [
  { "name": "Pam", "role": "ceo" },
  { "name": "Joel", "role": "engineer" },
  { "name": "Mary", "role": "ceo" },
  { "name": "Alice", "role": "analyst" },
  { "name": "John", "role": "analyst" },
  { "name": "Nick", "role": "engineer" },
  { "name": "Sam", "role": "analyst" }
]

预期产量：

Array2 = [
  { key: "ceo", count: 2 },
  { key: "engineer", count: 2 },
  { key: "analyst", count: 3 }
]

我需要一个从Array1生成Array2的代码。 非常感谢您的帮助:)

解决了我的问题，谢谢

Answer 1

应该相当简单易懂。 检查代码。

 let array1 = [ { name: "Pam", role: "ceo" }, { name: "Joel", role: "engineer" }, { name: "Mary", role: "ceo" }, { name: "Alice", role: "analyst" }, { name: "John", role: "analyst" }, { name: "Nick", role: "engineer" }, { name: "Sam", role: "analyst" } ]; let obj = {}; array1.forEach(entry => (obj[entry.role] = (obj[entry.role] || 0) + 1)); let array2 = []; for (role in obj) { array2.push({ key: role, count: obj[role] }); } console.log(array2); 

Answer 2

您可以使用reduce将对象数组分组为单个对象。 使用Object.values将对象转换回数组。

 let Array1 = [{"name":"Pam", "role":"ceo"}, {"name":"Joel", "role":"engineer"}, {"name":"Mary", "role":"ceo"}, {"name":"Alice", "role":"analyst"}, {"name":"John", "role":"analyst"}, {"name":"Nick", "role":"engineer"}, {"name":"Sam", "role":"analyst"}] let Array2 = Object.values(Array1.reduce((c, {role}) => { c[role] = c[role] || {key: role,count: 0}; c[role].count++; return c; }, {})); console.log(Array2); 

Answer 3

您必须创建一个哈希图/对象来跟踪唯一计数。

例如：

 let Array1=[{"name":"Pam", "role":"ceo"}, {"name":"Joel", "role":"engineer"}, {"name":"Mary", "role":"ceo"}, {"name":"Alice", "role":"analyst"}, {"name":"John", "role":"analyst"}, {"name":"Nick", "role":"engineer"}, {"name":"Sam", "role":"analyst"}] let hashMap = {} for(var employee of Array1){ //if that role exists if(employee.role in hashMap ){ //up the prev count hashMap[employee.role] = hashMap[employee.role] + 1; }else{ hashMap[employee.role] = 1; } } //now we will iterate through those keys of the Map and format it for Array 2 let outputArray = [] Object.keys(hashMap).forEach(key => { outputArray.push({ key, count: hashMap[key] }) }) console.log(outputArray) 

Answer 4

在这里，您有两个变体，分别是对象和数组。 （需要ES6）

 let arr = [ {"name":"Pam", "role":"ceo"}, {"name":"Joel", "role":"engineer"}, {"name":"Mary", "role":"ceo"}, {"name":"Alice", "role":"analyst"}, {"name":"John", "role":"analyst"}, {"name":"Nick", "role":"engineer"}, {"name":"Sam", "role":"analyst"} ] let objResult = arr.reduce((acc, obj) => { acc[obj.role] = (acc[obj.role] || 0) + 1; return acc; }, {}); console.log(objResult); let arrResult = Object.keys(objResult).map(k => ({[k]: objResult[k]})); console.log(arrResult)