list: from 2 to 3 dimensions..looking for a nice way

[Peter Otten]

Peter Otten wrote:

> sven wrote:
> 
>> I've got a nested list->
>> a = [[1,'house'],[2,'house'],[3,'garden']]
>> 
>> 
>> and I want to get one level deeper  with the lists having the same value
>> in index value 1
>> 
>> b =[[[1, 'house'], [2, 'house']], [[3, 'garten']]]
> 
> 
> How about:
> 
> a = [[1,'house'],[2,'house'],[3,'garden']]
> 
> d  = {}
> for n, s in a:
>     d.setdefault(s,[]).append(n)
> 
> b = [[[n, s] for n in nlist] for s, nlist in d.iteritems()]
> print b

Or rather

a = [[1,'house'],[2,'house'],[3,'garden']]

d  = {}
for ns in a:
    d.setdefault(ns[1], []).append(n)
b = d.items()

Peter