Python script 3

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
30,0.3
10,0.9

Command:
python script.py

Output:
key 10.0 finished
Traceback (most recent call last):
  File "script.py", line 13, in <module>
    result = np.vstack((result, col))
  File "/home/user/.local/lib/python2.7/site-packages/numpy/core/shape_base.py", line 234, in vstack
    return _nx.concatenate([atleast_2d(_m) for _m in tup], 0)
ValueError: all the input array dimensions except for the concatenation axis must match exactly