The Roll-Up Pattern vs the Bucket Pattern

Though I have completed this course with 96 grade I have to confess that I still do not see clear difference between the Roll Up and the Bucket patterns. As I see it both of them mean splitting the data into groups by some criteria (as they called in the video of the lecture on the Computed Pattern) or the buckets.
And Roll Up performs some aggregate calculations on those groups.
So it looks like the Bucket pattern is a precursor of the Roll up pattern. Am I wrong or right? Please share your vision on this matter