from collections import defaultdict

a = ([0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2])
  
b = ([0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 4.3, 0.1, 0.2, 0.3, 0.4, 0.6] )

group_dict = defaultdict( list )


# group every y by x
for x, y in zip(a, b):
    
    group_dict[x].append( y )


# calculate average value of each group
group_average = [ sum(group_dict[x])/len(group_dict[x]) for x in group_dict ]
    
# group id    
print( list( group_dict.keys() ) )

# group average
print( group_average )