If I have a list like this:
>>> data = [(1,2),(40,2),(9,80)]
how can I extract the the two lists [1,40,9] and [2,2,80] ? Of course I can iterate and extract the numbers myself but I guess there is a better way ?
-
1This isn't "extraction". This is sometimes called a "pivot". You're changing the structure of your list, not extracting a subset from it.S.Lott– S.Lott2009-03-20 11:24:46 +00:00Commented Mar 20, 2009 at 11:24
Add a comment
|
3 Answers
The unzip operation is:
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 on assignment:
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)
is equivalent to
zip((1,2), (40,2), (9,80))
The two tuples in the result list are built from the first elements of zip()'s arguments and from the second elements of zip()'s arguments.
Comments
List comprehensions save the day:
first = [x for (x,y) in data]
second = [y for (x,y) in data]
Comments
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)]
