newbie/ merging lists of lists with items in common

[Paddy]

On Feb 2, 1:55 pm, "ardief" <rachele.defel... at gmail.com> wrote:
> Hi everyone
> Here is my problem:
> I have a list that looks like this -
> [['a', '13'], ['a', '3'], ['b', '6'], ['c', '12'], ['c', '15'], ['c',
> '4'], ['d', '2'], ['e', '11'], ['e', '5'], ['e', '16'], ['e', '7']]
>
> and I would like to end up with something like this, i.e. with the
> only one list per letter:
>
> [['a', ['13' '3']], ['b', '6'], ['c', ['12', '15', '4']], ['d', '2'],
> ['e', ['11', '5', '16', '7']]]
>
> I have the feeling it's trivial, and I've scoured the group archives -
> sets might be a possibility, but I'm not sure how to operate on a list
> of lists with sets.
>
> This function also gives me what I want, more or less, but I don't
> know how to make it run until it's covered all the possibilities, if
> that makes sense...
>
> def sigh(list):
>         for a in list:
>                 i = list.index(a)
>                 if a != list[-1]:    ##if a is not the last one, i.e. there is a
> next one
>                         n = alist[i+1]
>                         if a[0] == n[0]:
>                                 a.append(n[1:])
>                                 del alist[i+1]
>
> Sorry about the lengthy message and thanks for your suggestions - I'm
> trying to learn...

: python
Python 2.5 (r25:51908, Nov 28 2006, 16:10:01)
[GCC 3.4.3 (TWW)] on sunos5
Type "help", "copyright", "credits" or "license" for more information.
>>> from pprint import pprint as pp
>>> from collections import defaultdict
>>> data = [['a', '13'], ['a', '3'], ['b', '6'], ['c', '12'], ['c', '15'], ['c', '4'], ['d', '2'], ['e', '11'], ['e', '5'], ['e', '16'], ['e', '7']]
>>> d = defaultdict(list)
>>> _ = [d[x0].append(x1) for x0,x1 in data]
>>> pp(d)
defaultdict(<type 'list'>, {'a': ['13', '3'], 'c': ['12', '15', '4'],
'b': ['6'], 'e': ['11', '5', '16', '7'], 'd': ['2']})
>>> pp(sorted(d.items()))
[('a', ['13', '3']),
 ('b', ['6']),
 ('c', ['12', '15', '4']),
 ('d', ['2']),
 ('e', ['11', '5', '16', '7'])]
>>>

- Paddy