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

[Peter Otten]

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

Peter