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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.
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To split a tuple, just list the variable names separated by commas on the left-hand side of an equals sign, and then a tuple on the right-hand side.
If you want to unzip your list of tuples, you use the combination of zip() method and * operator.
* operator unzips the tuples into independent lists. This is yet another way that can be employed to perform this task of unzipping which is less known but indeed a method to achieve this task. This also uses the * operator to perform the basic unpacking of the list. This function is deprecated in Python >= 3 versions.
copy. copy() and copy. deepcopy() just copy the reference for an immutable object like a tuple.
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
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