Creating a new data structure while filtering its data origin.

[Scott David Daniels]

mmara at fibertel.com.ar wrote:
> Hi everyone.
> 
> I'm trying to work with very simple data structures but I'm stuck in the very first steps. If someone has the luxury of a few minutes and can give an advice how to resolve this, I'll really appreciate it.
> 
> 1- I have a list of tuples like this:
> lista= [(162, 141, 3), (162, 141, 3), (162, 141, 3), (168, 141, 2), (168, 141, 2), (168, 141, 2), (201,  141, 1), (213, 141, 1), (203, 141, 1), (562, 142, 4), (562, 142, 4), (562, 142, 4), (568, 142, 2), (568, 142, 2), (568, 142, 2), (501,  142, 1), (513, 142, 1), (503, 142, 1)]
> and I want to end with a dict like this:
> {141: {1: [203, 213, 201], 2: [168, ], 3: [162, ]}, 142: {1: [503, 513, 501], 2: [568, ], 4: [562, ]}}
>  the logic of the final output:
>  a) the outer dict's key is a set() of the 2rd value of the input.
>  b) the inner dict's key is a set() of the 3th value for tuples which 3rd value equals a). 
>  c) the inner list will be fill up with the 1st value of every tuple which 3rd value equals b) and its 2rd value equals a).
> 
> So far, the only thing it seems I can achieve is the first part:
> outer_dict = dict([(x,dict()) for x in set(row[1] for row in lista)])
> 
>>From then on, I'm starting to get tired after several successful failures (I tried with itertools, with straight loops ...) and I don't know which can be the easier way to get that final output.
> 
> Thanks in advance.
> 
> 
     lista, wanted = ...
     result = {}
     for a,b,c in lista:
         inner = result.setdefault(b, {}).setdefault(c, [])
         if a not in inner:
             inner.insert(0, a)  # I had used append, but ...
     print result == wanted

--Scott David Daniels
scott.daniels at acm.org