Extract array from list in python

Question

If I have a list like this:

>>> data = [(1,2),(40,2),(9,80)]

how can i extract two lists [1,40,9] and [2,2,80]? Sure, I can iterate and extract numbers myself, but I think there is a better way?

Answer 1

Matching lists to save the day:

 first = [x for (x,y) in data] second = [y for (x,y) in data] 

Answer 2

Unpacking operation:

 In [1]: data = [(1,2),(40,2),(9,80)] In [2]: zip(*data) Out[2]: [(1, 40, 9), (2, 2, 80)] 

Edit: you can decompose the resulting list when assigning:

 In [3]: first_elements, second_elements = zip(*data) 

And if you really need lists as results:

 In [4]: first_elements, second_elements = map(list, zip(*data)) 

To better understand why this works:

 zip(*data) 

equivalently

 zip((1,2), (40,2), (9,80)) 

Two tuples in the list of results are constructed from the first elements of the zip () arguments and from the second elements of the zip () arguments.

Answer 3

There is also

 In [1]: data = [(1,2),(40,2),(9,80)] In [2]: x=map(None, *data) Out[2]: [(1, 40, 9), (2, 2, 80)] In [3]: map(None,*x) Out[3]: [(1, 2), (40, 2), (9, 80)]