Python script 2

Python script:
import numpy as np

data = np.genfromtxt('inputcsv', delimiter=',')
keys = sorted(set(data[:,0]))

result = np.array([])

for k in keys:
    col = data[np.where(data[:,0] == k)][:,1]
    if not result.any():
        result = col
    else:
        result = np.vstack((result, col))
    print('key {0} finished'.format(k))

np.savetxt('final.csv', np.transpose(result), delimiter=',')

Input file:
10,0.1
10,0.2
10,0.3
20,0.4
20,0.5
20,0.6

Command:
python script.py

Output:
key 10.0 finished
key 20.0 finished

Output file:
1.000000000000000056e-01,4.000000000000000222e-01
2.000000000000000111e-01,5.000000000000000000e-01
2.999999999999999889e-01,5.999999999999999778e-01