ValueError: setting an array element with a sequence (Python)

Question

I want to plot a CCDF graph in Python by reading data from a text file "data.txt". Anyway, I got an error "ValueError: setting an array element with a sequence".

Can anyone help me?

Here is my code in python:

import matplotlib.pyplot as plt
import numpy as np

read = np.loadtxt('data.txt')
with open('data.txt') as f:
    a = [map(float, line.split()) for line in f]

sorted=np.sort(a)

x2 = []
y2 = []
y = 0
for x in sorted: 
    x2.extend([x,x])
    print x2
    y2.append(y)
    y += 1.0 / len(a)
    y2.append(y)

plt.plot(x2,y2)
plt.show()

And here is my text file "data.txt":

9.500000000
2.500000000
3.500000000
4.500000000
6.500000000
1.500000000