如何使用TypeScript在Angular 2中对数据进行分组。我知道这是在Angular 1.X中使用“分组依据”过滤器完成的，但没有在Angular 2中获得如何对数据进行分组的方法。我有以下数组：
import {Employee} from './employee';
export var employees: Employee[];
employees = [
{ id: 1, firstName: "John", lastName: "Sonmez", department: 1, age: 24, address: "24/7, Working hours apartment, Cal. US", contactNumber: "+968546215789" },
{ id: 2, firstName: "Mark", lastName: "Seaman", department: 2, age: 25, address: "32-C, Happy apartments, Block-9C, Cal. US", contactNumber: "+968754216984" },
{ id: 3, firstName: "Jamie", lastName: "King", department: 3, age: 32, address: "54/II, Glorydale apartment, Cal. US", contactNumber: "+967421896326" },
{ id: 5, firstName: "Jacob", lastName: "Ridley", department: 5, age: 24, address: "24/7, Working hours apartment, Cal. US", contactNumber: "+968546215789" },
{ id: 6, firstName: "Peter", lastName: "Parker", department: 3, age: 25, address: "32-C, Happy apartments, Block-9C, Cal. US", contactNumber: "+968754216984" },
{ id: 7, firstName: "Martin", lastName: "Luther", department: 4, age: 32, address: "54/II, Glorydale apartment, Cal. US", contactNumber: "+967421896326" },
{ id: 8, firstName: "Raghav", lastName: "Kumar", department: 1, age: 34, address: "51/C Shivalik, Cal. US", contactNumber: "+967842569842" },
{ id: 9, firstName: "Narayan", lastName: "Sonmez", department: 3, age: 24, address: "24/7, Working hours apartment, Cal. US", contactNumber: "+968546215789" },
{ id: 10, firstName: "Russell", lastName: "Andre", department: 2, age: 25, address: "32-C, Happy apartments, Block-9C, Cal. US", contactNumber: "+968754216984" },
{ id: 11, firstName: "Ramona", lastName: "King", department: 4, age: 32, address: "54/II, Glorydale apartment, Cal. US", contactNumber: "+967421896326" },
{ id: 12, firstName: "Andre", lastName: "Russell", department: 1, age: 34, address: "51/C Shivalik, Cal. US", contactNumber: "+967842569842" },
{ id: 13, firstName: "Nathan", lastName: "Leon", department: 1, age: 24, address: "24/7, Working hours apartment, Cal. US", contactNumber: "+968546215789" },
{ id: 14, firstName: "Brett", lastName: "Lee", department: 5, age: 25, address: "32-C, Happy apartments, Block-9C, Cal. US", contactNumber: "+968754216984" },
{ id: 15, firstName: "Tim", lastName: "Cook", department: 2, age: 32, address: "54/II, Glorydale apartment, Cal. US", contactNumber: "+967421896326" },
{ id: 16, firstName: "Steve", lastName: "Jobs", department: 5, age: 34, address: "51/C Shivalik, Cal. US", contactNumber: "+967842569842" }
];
我希望按部门来统计员工人数，例如
部门1有4名员工
等等。
将部门ID与实际部门结合在一起（以便我可以获取部门名称）是我需要弄清楚的另一个故事。
我将创建一个自定义管道，如下所述：
@Pipe({name: 'groupBy'})
export class GroupByPipe implements PipeTransform {
transform(value: Array<any>, field: string): Array<any> {
const groupedObj = value.reduce((prev, cur)=> {
(prev[cur[field]] = prev[cur[field]] || []).push(cur);
return prev;
}, {});
return Object.keys(groupedObj).map(key => ({ key, value: groupedObj[key] }));
}
}
然后可以在模板上编写：
<div *ngFor="let item of employees | groupBy: 'department'">
Department {{ item.key }} has {{ item.value.length }} employees
</div>
另请参见相应的插件（https://plnkr.co/edit/49fWY1rMbSZtNQ3H）
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