Given N ranked ids lists of length P compute the number of extractions on topk positions and the mean position for each id. Sort the element ids with decreasing number of extractions, and element ids with equal number of extractions will be sorted with increasing mean positions.
Parameters : 


Returns : 

Example:
>>> import numpy as np
>>> import mlpy
>>> x = [[2,4,1,3,0], # first ranked list
... [3,4,1,2,0], # second ranked list
... [2,4,3,0,1], # third ranked list
... [0,1,4,2,3]] # fourth ranked list
>>> mlpy.borda_count(x=x, k=3)
(array([4, 1, 2, 3, 0]), array([4, 3, 2, 2, 1]), array([ 1.25 , 1.66666667, 0. , 1. , 0. ]))
 Id 4 is in the first position with 4 extractions and mean position 1.25.
 Id 1 is in the first position with 3 extractions and mean position 1.67.
 ...