How can I apply a quantity limit to *ngFor? [duplicate]

You can either apply an ngIf on the element using the index:

<div *ngFor=" let tweet of singleCategory;  let i=index">
    <div *ngIf="i<2">
        {{tweet}}
    </div>
</div>

If you don’t want the wrapping div, check out template syntax:

<ng-template ngFor let-tweet [ngForOf]="singleCategory" let-i="index">
    <div [ngIf]="i<2">
        {{tweet}}
    </div>
</ng-template>

Preferably you first/instead filter the elements in your component using filter to prevent unnecessary loops when displaying your data:

public get singleCategory() {
   return this.categories.filter((item, index) => index > 2 )
}

There is also the option of creating a pipe. (See the linked duplicate)