The shelf can be sorted by Recently Updated, Recently Added, and alphabetically by Name by clicking on the gear icon to the left of the Search bar.
Clicking the icon will remove everything from the Bucket Shelf view except for icon (which indicates how the dataset originated) and the bucket name. This allows more buckets to be viewed at a time.
Clicking the icon will keep the shelf open, overriding the auto-hide that happens when you select a visualization app.
NOTE: The icon is for uploading files, which is a feature only available to Pro Users.