How to unzip a list of tuples into individual lists?

Possible Duplicate:
A Transpose/Unzip Function in Python

I have a list of tuples, where I want to unzip this list into two independent lists. I’m looking for some standardized operation in Python.

>>> l = [(1,2), (3,4), (8,9)]
>>> f_xxx (l)
[ [1, 3, 8], [2, 4, 9] ]

I’m looking for a succinct and pythonic way to achieve this.

Basically, I’m hunting for inverse operation of zip() function.

Answers:

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Method 1

Use zip(*list):

>>> l = [(1,2), (3,4), (8,9)]
>>> list(zip(*l))
[(1, 3, 8), (2, 4, 9)]

The zip() function pairs up the elements from all inputs, starting with the first values, then the second, etc. By using *l you apply all tuples in l as separate arguments to the zip() function, so zip() pairs up 1 with 3 with 8 first, then 2 with 4 and 9. Those happen to correspond nicely with the columns, or the transposition of l.

zip() produces tuples; if you must have mutable list objects, just map() the tuples to lists or use a list comprehension to produce a list of lists:

map(list, zip(*l))          # keep it a generator
[list(t) for t in zip(*l)]  # consume the zip generator into a list of lists

Method 2

If you want a list of lists:

>>> [list(t) for t in zip(*l)]
[[1, 3, 8], [2, 4, 9]]

If a list of tuples is OK:

>>> zip(*l)
[(1, 3, 8), (2, 4, 9)]

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