set of sets

Matteo Dell'Amico della at
Thu Aug 11 16:18:47 CEST 2005

Paolo Veronelli wrote:

> And mostly with sets remove operation expense should be sublinear or am
> I wrong?
> Is this fast as with lists?

It's faster then with lists... in sets, as with dicts, remove is on 
average O(1).

> Obviously if I use the ids as hash value nothing is guaranted about the
> objects contents to be unique but I don't care.
> My work is a self organizing net,in which the nodes keep a structure to
> link other nodes.As the nature of the net,the links are moved frequently
>  so remove and add operations and contains query should be optimized.
> Why objects need to be hashable for this? Isn't __hash__ there to solve
> the problem?

The idea of a set of mutable sets looks a bit odd to me...
I don't get why the outer container should be a set, since you don't 
care about uniqueness... if you are representing a graph (which seems 
the case to me), I'd use an identifier for each node, and a dictionary 
mapping node-ids to its adjacency set for each node. For instance,

0 <-- 1 --> 2 --> 3
             |     |
             v     v
             4 --> 5

would be represented as

{0: set([]), 1: set([0, 2]), 2: set([2,4]), 3: set([5]), 4: set([5]),
  5: set([])}

If node ids are consecutive integers, you could also of course use a 
list as the outer structure.

PS: we could also discuss this in italian in it.comp.lang.python :)


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