create dictionary from lists in python : I have two lists in python of the following structure:

        [[x1,y1],[x2,y2],[x3,y3],[x4,y4],[x5,y5],[x6,y6],[x7,y7],[x8,y8]] ,    [1,1,2,2,3,3,3,4]

And I want to create a dictionary with keys of the second list and values of the first list, that looks like this:

     {1: [[x1,y1], [x2,y2]], 2: [[x3,y3],[x4,y4]] , 3: [[x5,y5],[x6,y6],[x7,y7]], 4:[x8,y8]}

What is the most efficient way to do this in python?