RXJS Groupby on Observable / Array

Question

I have an observable that contains an array of news article objects that i wish to group by date, so that i can use it in my template.

I've read about the groupBy operator, but i can't get it working yet. I've set up an array that i fill with the items array in my Observable:

    export class NewsArchiveComponent implements OnInit {

  archivedNews$: Observable<NewsItemPage> | undefined;
  newsItems: NewsItem[] = [];

  constructor(private newsService: NewsService) { }

  ngOnInit(): void {
    this.archivedNews$ = this.newsService.newsPerYear();
    this.fillNewsArray();
  }

  fillNewsArray() {
    this.archivedNews$?.subscribe(x => {
      this.newsItems = x.items;
      console.log(x);
      console.log(this.newsItems);
    });
  }
}

I have tried the following to group my items, but it didn't work, neither did it log to console:

groupNewsItems() {
    of(this.newsItems)
      .pipe(
        concatMap(res => res),
        groupBy(item => item.publicationdate),
        mergeMap(group => zip(of(group.key), group.pipe(toArray())))
      )
      .subscribe(console.log);
  }

Answer 1

Use from instead of of and try the following:

import { from, of, zip } from 'rxjs';
import { groupBy, mergeMap, toArray } from 'rxjs/operators';

from(this.newsItems)
  .pipe(
    concatMap(res => res),
    groupBy(
     item => item.publicationdate
    ),
    mergeMap(group => zip(of(group.key), group.pipe(toArray())))
)
.subscribe(console.log);