34 – Transpose a list of lists

34 – Transpose a list of lists#

The built-in zip can be used with the splat operator * to transpose a list of iterables.

For example, you can go from

persons = [["Han", "Solo"], ["Obi-Wan", "Kenobi"], ["Darth", "Vader"]]

to

firsts = ('Han', 'Obi-Wan', 'Darth')
lasts = ('Solo', 'Kenobi', 'Vader')

You just need a simple line of code:

firsts, lasts = zip(*persons)

If you look closely, this is zip undoing what zip can do, since you can recreate persons by doing zip(firsts, lasts):

print(list(zip(firsts, lasts)))
# [('Han', 'Solo'), ('Obi-Wan', 'Kenobi'), ('Darth', 'Vader')]

The only thing to note is that zip produces tuples, so the original variable persons contained a list of lists and the output from the snippet above is a list of tuples.