Question

I have a list of lists like this:

a = d[:3]
>>> a
[[90, 26.7328829998, 131075.449348, 473898.809493],
 [90, 78.2985549184, 131116.812991,473929.491012],
 [90, 132.4760969, 131157.881628, 473964.821961]]

To change it’s order I use the BIF zip in combination with the *-operator. This get’s me a list of tuples:

>>> b =zip(*a)
>>> b
[(90, 90, 90),
 (26.7328829998, 78.2985549184, 132.4760969),
 (131075.449348, 131116.812991, 131157.881628),
 (473898.809493, 473929.491012, 473964.821961)]

I don’t only want to restore the original order of the items, like:

>>> c = zip(*b)
>>> c
[(90, 26.7328829998, 131075.449348, 473898.809493),
 (90, 78.2985549184, 131116.812991, 473929.491012),
 (90, 132.4760969, 131157.881628, 473964.821961)] 

but also want to get back the original type, e.g. a list of lists. But neither zip(*list(b)) nor list(zip(*b)) do the trick (I wasn’t expecting the second snippet to). Does anyone know how to get there without looping through the list!?

Answer 1

izip returns a generator so you won’t loop through twice when you create c. In Python 3 zip (also map, filter, etc.) returns a generator by default and izip has been removed.

>>> from itertools import izip
>>> a = [[90, 26.7328829998, 131075.449348, 473898.809493], [90, 78.2985549184, 131116.812991,473929.491012], [90, 132.4760969, 131157.881628, 473964.821961]]
>>> b = zip(*a)
>>> c = map(list, izip(*b))
>>> c
[[90, 26.7328829998, 131075.449348, 473898.809493], [90, 78.2985549184, 131116.812991, 473929.491012], [90, 132.4760969, 131157.881628, 473964.821961]]