f_diff = f_sort[list(pos_columns) + ["particle", "frame"]].diff()
// Rename the frame column and insert the original frame column back in.f_diff.rename(columns={"frame": "frame_diff"}, inplace=True)
f_diff["frame"] = f_sort["frame"]
// Compute the per frame averages. Keep only deltas of the same particle,// and between frames that are consecutive, and of the same particle.