How to find the maximum date from an array?

Question

Angular

Based on the condition, how to display one value at a certain interval. All users currently displayed if user.dateless than or equal to report.report_date. But we need to display only the user who will be closest to the value in the interval. That is, how to display the maximum date for user.datein order for the condition to work.

<div *ngFor="let report  of reports">
   <div *ngFor="let user  of users">
      <div *ngIf="report.users_id==user.user_id">
         <div *ngIf="report.report_date >= user.date">
            {{user.name}}
         </div>
       </div>
   </div>
</div>

TS:

users: User[]
reports: Report[]

  private loadUsers() {
    this.usersService.fetch().subscribe(
      users => {
        this.users = users;
      }
    );
  }

 private loadReports() {
    this.reportsService.fetch().subscribe(
      reports => {
        this.reports = reports
      }
    )
  }

Answer 1

Maybe something like this, but I haven't tested it.

// шаблон
<div *ngFor="let user of reportsWithUser$|async">
    {{user.name}}
</div>

//компонент
import {Observable} from "rxjs";
import {map, switchMap} from "rxjs/operators";
import * as _ from 'underscore';

interface User {
    user_id: number;
    name: string;
    date: string;
}
interface Report {
    report_date: string;
    users_id: number;
}
interface UserWithReports extends User {
    reports: Report[];
    reportWithMaxDate: Report;
}

export function assignReportToUser(user: User, reports: Report[]): UserWithReports {
    const repFiltered = reports.filter(report => report.report_date >= user.date);
    return {...user, reports: repFiltered.filter(report => report.users_id === user.user_id), reportWithMaxDate: _.max(repFiltered, (r) => r.report_date)};
}

export class AnyComponent {
    reportsWithUser$: Observable<UserWithReports[]>;
    constructor(
        public reportsService: any,
        public usersService: any
    )  {
        this.reportsWithUser$ = this.reportsService.fetch().pipe(
            switchMap((reports: Report[]) => this.usersService.fetch().pipe(
                    map((users: User[]) => {
                        return users.map(user => assignReportToUser(user, reports)).filter((user) => user.reportWithMaxDate !== null);
                    })
                )
            )
        )
    }
}