Question

I have a list in python. This list has sublist in it.
for example:

 [['85.', 'Document', 'will', 'discuss', 'allegations,', 'or', 'measures', 'being', 'taken', 'against,', 'corrupt', 'public', 'officials', 'of', 'any', 'governmental', 'jurisdiction', 'worldwide.'], ['56.', 'Document', 'will', 'include', 'a', 'prediction', 'about', 'the', 'prime', 'lending', 'rate,', 'or', 'will', 'report', 'an', 'actual', 'prime', 'rate', 'move.'], and so on]

when i print mylist[0], i get the following:

['85.', 'Document', 'will', 'discuss', 'allegations,', 'or', 'measures', 'being', 'taken', 'against,', 'corrupt', 'public', 'officials', 'of', 'any', 'governmental', 'jurisdiction', 'worldwide.']

when i print mylist[0][0] i get 85.

I am new to python and i dont understand how to access these values(85, 56, and so on) inside a for loop, so that i can delete all the numbers. i.e 85, 56, and so on.

1. Also I have a similar list [[1, 23], [2, 34], [3, 45], [1, 45], [2, 44]]
   and i want to add all the second elements where the 1st element is the same. i.e i want to add 23 + 45 (because both have 1 as their 1st element). I understand i need a for loop, but i am new to python, and i am not able to understand the loops.

Answer 1

To get all the first elements:

zip(*your_list)[0]

zip(*some_iterable) does some kind of matrix inversion – you should play a bit with it to get an idea.

To remove all the first values from a set of iterables you may choose a few ways. E.g.:

[item[1:] for item in your_list]  # probably the best
zip(*zip(*your_list)[1:])  # tricky and probably slow one

To sum your values you’d need a dictionary:

>>> from collections import defaultdict
>>> l = [[1, 23], [2, 34], [3, 45], [1, 45], [2, 44]]
>>> d = defaultdict(int)
>>> for item in l:
    d[item[0]] += item[1]

>>> d.items()
[(1, 68), (2, 78), (3, 45)]

We use defaultdict here to be able to perform this d[item[0]] += item[1] assigment. With simple dict we’d get a KeyError, since our d is empty. But defaultdict in this case just returns default value – int(), which is 0.