[erlang-questions] Bug in sets module? Equal sets aren't equal

Hugo Mills <>
Mon Feb 20 16:21:18 CET 2017


On Mon, Feb 20, 2017 at 03:32:56PM +0100,  wrote:
> Hello.
> 
> What about this:
> 
> sets:size(S1) == sets:size(S2) andalso sets:is_subset(S1, S2)
> 
> ?
> 
> This seems rather elegant, at least to me :-)

   It was my fallback solution, too.

> Note however that I am not sure what the function sets:is_subset/2 returns for two empty sets (I do not have Erlang available at the moment to test it).

1> sets:is_subset(sets:new(), sets:new()).
true

so that edge case works, too.

   Hugo.

> HTH,
> 
> Ladislav Lenart
> 
> 
> ______________________________________________________________
> > Od: "Alex S." <>
> > Komu: Hugo Mills <>
> > Datum: 20.02.2017 15:11
> > Předmět: Re: [erlang-questions] Bug in sets module? Equal sets aren't equal
> >
> > CC: <>
> >
> >> 20 февр. 2017 г., в 16:58, Hugo Mills <> написал(а):
> >> 
> >> sets:from_list([[2, 2], [2, -2]]) =:= sets:from_list([[2, -2], [2, 2]]).
> >
> >The onyl way to compare them for equality would be elementwise anyway, i.e. I'd roll with sets:to_list, it’s about as optimal as it gets.
> >
> >----------
> >
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> >
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> >
> >

-- 
Hugo Mills             | Great films about cricket: Umpire of the Rising Sun
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