accessing python 2D array

Question

suppose we have:

a = [[1, 2, 3], [4, 5, 6]]

What is the fastest way to access the array such that we get the first element in each list, other than looping.

i would like the result to be giving me... 1,4

Answer 1

using zip(*a)

a = [[1, 2, 3], [2, 3, 4]]
result = zip(*a)[0]
print result

Answer 2

A quick and easy way is to just extract a[0][0] and a[1][0], but depending on what you are using it for, this might not work all the time.

Answer 3

Without looping, you need to unroll the loop as ethg242 does. This has the disadvantage of only working for a fixed length of a

Here is a list comprehension

[i[0] for i in a]

It's also possible to use map(), but this also has an implicit loop

from operator import itemgetter
map(itemgetter(0), a)

Answer 4

You might want to consider numpy:

>>> import numpy as np
>>> a = [[1, 2, 3], [4, 5, 6]]
>>> b = np.array(a)
>>> b[:,0]
array([1, 4])