import numpy as np
import matplotlib.pyplot as plt
import scipy.cluster.hierarchy as sch
from sklearn.cluster import AgglomerativeClustering
gradesy=np.array([94.28379291,86.98982195,86.63611546,85.7203357,84.52017914,83.11406572,82.5180994,80.0522343,77.76367201,76.87708018,74.87290704,74.43641397,70.92109845,70.74501915,69.955087,68.72333003,67.43377364,65.31794233,65.19391681,64.07626518,46.06843416])
gradesx=np.zeros(gradesy.size)
grades=np.concatenate((gradesx.reshape(gradesy.size,1),gradesy.reshape(gradesy.size,1)),axis=1)
plt.scatter(grades[:,0], grades[:,1], s=100)