Swift 3, CollectionView, Scroll
let x = yourArray.count - 1
let y = NSIndexPath(item: x, section: 0)
collectionView.scrollToItem(at: y as IndexPath, at: .bottom, animated: true)
OR
collectionView.contentOffset.y = (400)
self.collectionView.scrollToItemAtIndexPath(NSIndexPath(forItem: yourArray.count, inSection: 0), atScrollPosition: .Bottom, animated: true)