假设我有以下内容:
var array =
[
{"name":"Joe", "age":17},
{"name":"Bob", "age":17},
{"name":"Carl", "age": 35}
]
获得所有不同年龄的数组的最佳方法是什么，这样我就得到了一个结果数组:
[17, 35]
是否有一些方法，我可以选择结构数据或更好的方法，这样我就不必遍历每个数组检查“年龄”的值，并检查另一个数组是否存在，如果没有添加它?
如果有某种方法可以让我不用迭代就能得到不同的年龄……
目前效率低下的方式，我想改进…如果它的意思不是“数组”是一个对象的数组，而是一个对象的“映射”与一些唯一的键(即。"1,2,3")也可以。我只是在寻找最高效的方式。
以下是我目前的做法，但对我来说，迭代似乎只是为了提高效率，即使它确实有效……
var distinct = []
for (var i = 0; i < array.length; i++)
if (array[i].age not in distinct)
distinct.push(array[i].age)
清洁解决方案
export abstract class Serializable<T> {
equalTo(t: Serializable<T>): boolean {
return this.hashCode() === t.hashCode();
}
hashCode(): string {
throw new Error('Not Implemented');
}
}
export interface UserFields {
firstName: string;
lastName: string;
}
export class User extends Serializable<User> {
constructor(private readonly fields: UserFields) {
super();
}
override hashCode(): string {
return `${this.fields.firstName},${this.fields.lastName}`;
}
}
const list: User[] = [
new User({ firstName: 'first', lastName: 'user' }),
new User({ firstName: 'first', lastName: 'user' }),
new User({ firstName: 'second', lastName: 'user' }),
new User({ firstName: 'second', lastName: 'user' }),
new User({ firstName: 'third', lastName: 'user' }),
new User({ firstName: 'third', lastName: 'user' }),
];
/**
* Let's create an map
*/
const userHashMap = new Map<string, User>();
/**
* We are adding each user into the map using user's hashCode value
*/
list.forEach((user) => userHashMap.set(user.hashCode(), user));
/**
* Then getting the list of users from the map,
*/
const uniqueUsers = [...userHashMap.values()];
/**
* Let's print and see we did right?
*/
console.log(uniqueUsers.map((e) => e.hashCode()));
var unique = array
.map(p => p.age)
.filter((age, index, arr) => arr.indexOf(age) == index)
.sort(); // sorting is optional
// or in ES6
var unique = [...new Set(array.map(p => p.age))];
// or with lodash
var unique = _.uniq(_.map(array, 'age'));
ES6例子
const data = [
{ name: "Joe", age: 17},
{ name: "Bob", age: 17},
{ name: "Carl", age: 35}
];
const arr = data.map(p => p.age); // [17, 17, 35]
const s = new Set(arr); // {17, 35} a set removes duplications, but it's still a set
const unique = [...s]; // [17, 35] Use the spread operator to transform a set into an Array
// or use Array.from to transform a set into an array
const unique2 = Array.from(s); // [17, 35]
