[erlang-questions] Sets from list then to list?

Alexander Lamb <>
Mon Apr 7 11:57:35 CEST 2008

```Well, spoke to fast. usort/1 works fine, but when I provide my own
function, it doesn't remove the duplicates.
It looks like this is because my sort function can only return true or
false. What should it return to usort/2 removes correctly duplicates.

Thanks,

Alex

Le 7 avr. 08 à 11:18, Alexander Lamb a écrit :
> Thanks, usort(Fun, List) is the solution!
>
> (I need to sort according to my own algorithm)
>
> Alex
>
> Le 7 avr. 08 à 11:07, Hynek Vychodil a écrit :
>>
>>
>> On Mon, Apr 7, 2008 at 10:51 AM, Kostis Sagonas <>
>> wrote:
>> Alexander Lamb wrote:
>>> Hello (list:-)
>>>
>>> Using list comprehension, I am building a list of tuples that I want
>>> unique and sorted.
>>>
>>> Is this a correct way of doing it:
>>>
>>> Result = sets:to_list(sets:from_list([ {A,B} || {_X,_Y,A,_Z,B} <-
>>> MyList]))
>>>
>>> Then sort the Result.
>>>
>>> The alternative would be to use one of the lists functions to copy
>>> elements into a new list and testing first at each insert if the
>>> element is already present.
>>>
>>> What is best?
>>
>> None of the two.  Check out lists:usort/1.
>>
>> 1> lists:usort([{1,2},{1,3},{0,1},{1,2}]).
>> [{0,1},{1,2},{1,3}]
>>
>> Yup, faster one :-)
>>
>>
>> Kostis
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>>
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>>
>>
>>
>> --
>> --Hynek (Pichi) Vychodil
>
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```