I've been using Wunderlist for some time. It is a great tool especially when it comes to group shopping. I've seen a lot of people posting questions on how to "group unselect" items on wunderlist. It was even on the "most requested feature-list". I found a way to do this in 3 super quick steps- so sharing it below: Press CTRL+A to select all items (Ensure the completed items are hidden - this should be default) and then Press CTRL+D to mark them as completed. Now all items should be hidden since they are marked as complete. Now click 'Show marked items' to show them all. CTRL+A to select all and CTRL+D to mark them incomplete. This has really helped me with my grocery lists since I would need to reset it before the next purchase.