[Tutor] Flatten a list in tuples and remove doubles

[Dave Angel]

On 07/28/2012 07:12 PM, Francesco Loffredo wrote:
> Il 28/07/2012 20:41, eryksun wrote:
>> On Sat, Jul 28, 2012 at 11:12 AM, Francesco Loffredo<fal at libero.it> 
>> wrote:
>>> I had to study carefully your present and desired lists, and I
>>> understood
>>> what follows (please, next time explain !):
>>> - each 7-tuple in your present list is a record for some measure
>>> relative to
>>> a person. Its fields are as follows:
>>>      - field 0: code (I think you want that in growing order)
>>>      - field 1: group code (could be a class or a group to which
>>> both of your
>>> example persons belong)
>>>      - fields 2, 3: surname and name of the person
>>>      - field 4: progressive number of the measure (these are in order
>>> already, but I think you want to enforce this) that you want to
>>> exclude from
>>> the output list while keeping the order
>>>      - field 5, 6: numerator and denominator of a ratio that is the
>>> measure.
>>> you want the ratio to be written as a single string: "%s/%s" % field5,
>>> field6
>> This looks like a good problem for itertools.groupby. My solution
>> below needs error checking and testing, but this is where I'd start:
>>
>> data = [
>>    (0, '3eA', 'Dupont', 'Juliette', 0, 11.0, 10.0),
>>    (0, '3eA', 'Dupont', 'Juliette', 1, 4.0, 5.0),
>>    (0, '3eA', 'Dupont', 'Juliette', 2, 17.5, 30.0),
>>    (0, '3eA', 'Dupont', 'Juliette', 3, 3.0, 5.0),
>>    (0, '3eA', 'Dupont', 'Juliette', 4, 4.5, 10.0),
>>    (0, '3eA', 'Dupont', 'Juliette', 5, 35.5, 60.0),
>>    (1, '3eA', 'Pop', 'Iggy', 0, 12.0, 10.0),
>>    (1, '3eA', 'Pop', 'Iggy', 1, 3.5, 5.0),
>>    (1, '3eA', 'Pop', 'Iggy', 2, 11.5, 30.0),
>>    (1, '3eA', 'Pop', 'Iggy', 3, 4.0, 5.0),
>>    (1, '3eA', 'Pop', 'Iggy', 4, 5.5, 10.0),
>>    (1, '3eA', 'Pop', 'Iggy', 5, 40.5, 60.0),
>> ]
>>
>> from operator import itemgetter
>> from itertools import groupby
>>
>> #first sort by keyfunc, then group by it
>> keyfunc = itemgetter(0,1,2,3)
>> groups = groupby(sorted(data, key=keyfunc), keyfunc)
>>
>> result = []
>> for group, records in groups:
>>      temp = tuple('%s/%s' % r[5:] for r in sorted(records,
>> key=itemgetter(4)))
>>      result.append(group + temp)
>>
>>>>> result
>> [(0, '3eA', 'Dupont', 'Juliette', '11.0/10.0', '4.0/5.0', '17.5/30.0',
>> '3.0/5.0', '4.5/10.0', '35.5/60.0'), (1, '3eA', 'Pop', 'Iggy',
>> '12.0/10.0', '3.5/5.0', '11.5/30.0', '4.0/5.0', '5.5/10.0',
>> '40.5/60.0')]
>>
> Hmmmm... it happened again. I spend some time and effort to solve a
> problem, I feel like I'm almost a Real Python Programmer... and
> someone spoils my pride showing me some standard module whose name I
> barely remember, that can solve that same problem in a few lines...
>
> Hey! That's a GREAT solution, Eryksun! Nothing wrong with you, really!
>
> Every time this happens, I have to admit that I'm a newbie and I've
> still got a lot to learn about Python. Especially about its wonderful
> standard library. Better than Apple's App Store: for anything you can
> think, there's a Module. Problem is, I still can't readily recall
> which to use for a given problem.
> My bad, now I'll RTFM again and I will study very carefully the
> operator and itertools modules. Who knows, maybe in a few decades I'll
> be able to say "This looks like a good problem for Module X" too.
>
> Francesco
>

You might find it enlightening to look up:

    http://www.doughellmann.com/PyMOTW/

which explores the Pythons standard library.

-- 

DaveA