I have a datapack that has a book to summon wither skulls and when it is summoned it needs to go to the direction the player is facing.
The problem is that the way wither skulls get their direction set is by using a list called "power" which is a 3d vector unlike the player's Rotation which is a set of angles.
I thought I could make it if I could get data from player and run it through a sine function but the thing is both of the objects are lists and I do not know how to get specific elements from lists nor how to overwrite them from scoreboards so I need help.

In short; how do I take a player's Rotation and turn it into power for a wither skull?