Question

i have a numpy array like the following

[[ 1 2 3 4 ]
 [ 5 6 7 8 ] 

......... ]

So basically I want to create 4 (can be different) lists where

 list_1 = [1,5...], list_2 = [2,6....] and so on.

What is the pythonic way to do this?

Answer 1

Given a numpy array

>>> numpy.array([[x for x in xrange(i,i+5)] for i in xrange(0,100,10)])
array([[ 0,  1,  2,  3,  4],
       [10, 11, 12, 13, 14],
       [20, 21, 22, 23, 24],
       [30, 31, 32, 33, 34],
       [40, 41, 42, 43, 44],
       [50, 51, 52, 53, 54],
       [60, 61, 62, 63, 64],
       [70, 71, 72, 73, 74],
       [80, 81, 82, 83, 84],
       [90, 91, 92, 93, 94]])

You first have to transpose it

>>> narray=numpy.array([[x for x in xrange(i,i+5)] for i in xrange(0,100,10)])
>>> tarray=numpy.transpose(narray)
array([[ 0, 10, 20, 30, 40, 50, 60, 70, 80, 90],
       [ 1, 11, 21, 31, 41, 51, 61, 71, 81, 91],
       [ 2, 12, 22, 32, 42, 52, 62, 72, 82, 92],
       [ 3, 13, 23, 33, 43, 53, 63, 73, 83, 93],
       [ 4, 14, 24, 34, 44, 54, 64, 74, 84, 94]])

and then convert to list

>>> larray=tarray.tolist()
>>> larray
[[0, 10, 20, 30, 40, 50, 60, 70, 80, 90], [1, 11, 21, 31, 41, 51, 61, 71, 81, 91], [2, 12, 22, 32, 42, 52, 62, 72, 82, 92], [3, 13, 23, 33, 43, 53, 63, 73, 83, 93], [4, 14, 24, 34, 44, 54, 64, 74, 84, 94]]

now you can index larray as larray[0], larray[1] to get the individual lists.