Python matplotlib eksendeki verileri özetleme

import matplotlib.pyplot as plt
import numpy as np
f = open("dolarvalue.txt" ,"r")
xtwo = (f.readlines())
arr_2 = np.array(xtwo)
ln = len(arr_2)
array = []
for i in range(0,ln):
 array.append(arr_2[i])
plt.plot(range(0,ln),array)
plt.show()