Python - How to sort a list of lists by the fourth element in each list?

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Sort a list of tuples by 2nd item (integer value) [duplicate] (9 answers)

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I would like to sort the following list of lists by the fourth element (the integer) in each individual list.

unsorted_list = [['a','b','c','5','d'],['e','f','g','3','h'],['i','j','k','4','m']]

How can I do this? Thank you!

Answer 1

unsorted_list.sort(key=lambda x: x[3])

Answer 2

Use sorted() with a key as follows -

>>> unsorted_list = [['a','b','c','5','d'],['e','f','g','3','h'],['i','j','k','4','m']]
>>> sorted(unsorted_list, key = lambda x: int(x[3]))
[['e', 'f', 'g', '3', 'h'], ['i', 'j', 'k', '4', 'm'], ['a', 'b', 'c', '5', 'd']]

The lambda returns the fourth element of each of the inner lists and the sorted function uses that to sort those list. This assumes that int(elem) will not fail for the list.

Or use itemgetter (As Ashwini's comment pointed out, this method would not work if you have string representations of the numbers, since they are bound to fail somewhere for 2+ digit numbers)

>>> from operator import itemgetter
>>> sorted(unsorted_list, key = itemgetter(3))
[['e', 'f', 'g', '3', 'h'], ['i', 'j', 'k', '4', 'm'], ['a', 'b', 'c', '5', 'd']]