How to solve the trackBy problem if there are duplicate values in the array and no unique identifier?

If there are duplicate values in an array and no unique identifier, you can use the index of the element in the array for trackBy in Angular or similar frameworks. This helps avoid issues with duplicate values, as the index is unique for each position.

Example of using trackBy with index:

<div *ngFor="let item of items; let i = index; trackBy: trackByIndex">
  {{ item }}
</div>

trackByIndex(index: number, item: any): number {
  return index;
}

The downside of this approach is that if the order of elements changes, Angular will consider them different, which may lead to re-rendering the entire list. If this is critical, you can try to create a composite key from multiple properties of the element, if available, or add a temporary unique identifier when loading data.