Data output by the filter when the page loads using angular4 + firebase?

Good afternoon, the problem is in the different columns need to display different data from firebase based on their 'size'
the structure of the database
size: small
text: "First text"
size: medium
text: "Second text"

html file
li class="text" *ngFor="let item of items | async"

and component
items: FirebaseListObservable;
item: FirebaseObjectObservable;
sizeSubject: Subject;

constructor(private http: TransferHttp, af: AngularFire) {
this.sizeSubject = new Subject();
this.items = af.database.list('/items', {
// query: {
// orderByChild: 'size',
// with equalto: this.sizeSubject
// }
filterBy(size: string) {;

How can I bring in ngFor all the elements from 'size' = 'small' example. Commented lines help to arrange the filter when you click, but it then displays nothing
In advance thank you very much
June 27th 19 at 15:01

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