You can either apply an ngIf on the element using the index:
If you don't want the wrapping div, check out template syntax:
{{tweet}}
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)