DeleteAndInsert.swift

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
      if collectionView == baseCollectionView {
          let alphabetLetter = baseCollectionViewArray[indexPath.item]
          secondCollectionViewArray.append(alphabetLetter)
          let newIndexPath = IndexPath(item: secondCollectionViewArray.count - 1, section: 0)
          secondCollectionView.insertItems(at: [newIndexPath])
          ///First, add a cell to the second collectionview.

          baseCollectionViewArray.remove(at: indexPath.item)
          baseCollectionView.deleteItems(at: [indexPath])
          ///Now, remove it from the base collectionview.
      }
}