Does Set respect ordering?

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tty
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Does Set respect ordering?

tty
Hi Folks.


If I have an OrderedCollection and convert it to Set via asSet, am I
guaranteed that the resulting Set contains elements in the same order as the
OrderedCollection?

Here is my problem.

I have an OrderedCollection with the same element in it twice. By same
element, I mean they are the same object.

*an OrderedCollection(
A
NESTED  TABLE CELL
 
B
A
NESTED  TABLE CELL

)
*

Above, the first and third elements are the same XMLElement. I now this
because if I inspect them and then change one, the other changes.

if I run asSet on the OrderedCollection, I get what I need:

*a Set( A
NESTED  TABLE CELL
 
B)*


In that conversion, can I rely on that Ordering being preserved?

If not, a pointer to the correct select/reject/inject/detect...sort of thing
would be much appreciated.

cheers.







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Re: Does Set respect ordering?

Christoph Thiede

Hi tty,


Set does not guarantee the order of elements. It's an implementation detail. If you only need to remove duplicates, have a look at #withoutDuplicates.


Does this help? :-)

Best,
Christoph

Von: Beginners <[hidden email]> im Auftrag von tty <[hidden email]>
Gesendet: Dienstag, 11. Februar 2020 16:07:15
An: [hidden email]
Betreff: [Newbies] Does Set respect ordering?
 
Hi Folks.


If I have an OrderedCollection and convert it to Set via asSet, am I
guaranteed that the resulting Set contains elements in the same order as the
OrderedCollection?

Here is my problem.

I have an OrderedCollection with the same element in it twice. By same
element, I mean they are the same object.

*an OrderedCollection(
A
NESTED  TABLE CELL
 
B
A
NESTED  TABLE CELL

)
*

Above, the first and third elements are the same XMLElement. I now this
because if I inspect them and then change one, the other changes.

if I run asSet on the OrderedCollection, I get what I need:

*a Set( A
NESTED  TABLE CELL
 
B)*


In that conversion, can I rely on that Ordering being preserved?

If not, a pointer to the correct select/reject/inject/detect...sort of thing
would be much appreciated.

cheers.







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[hidden email]
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tty
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Re: Does Set respect ordering?

tty
Christoph

Perfect! thank you!.





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Re: Does Set respect ordering?

tty
In reply to this post by Christoph Thiede
The implementation of withoutDuplicates is brilliant.


*withoutDuplicates
        "Answer a copy of the receiver that preserves order but eliminates any
duplicates."
        | seen |
        seen := Set new: self size.
        ^self select: [:each| seen ifAbsentAdd: each]*

The Set acts as a growing "mask" of what is allowed in the OrderedCollection
returned by select.

I have never seen this idiom. Truly inspiring.




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Re: Does Set respect ordering?

Nicola Mingotti
In reply to this post by Christoph Thiede

Hi,

The "set" is a mathematical object which is defined by what it contains, there isn't any order concept in it.

So, by definition of set: {1,2,3} = {2,3,1}

It makes not even sense to ask what is the first element of a set, because there is no order in it.

So, I guess Christoph is giving you the right hint, keep working with OrderedCollection.

Then, you may open your Squeak, on top of the Window select Help -> Terse Guide To Squeak
and check ouy "Bag" and "Set" sections.

bye
n.



On 2/11/20 7:11 AM, Thiede, Christoph wrote:

Hi tty,


Set does not guarantee the order of elements. It's an implementation detail. If you only need to remove duplicates, have a look at #withoutDuplicates.


Does this help? :-)

Best,
Christoph

Von: Beginners [hidden email] im Auftrag von tty [hidden email]
Gesendet: Dienstag, 11. Februar 2020 16:07:15
An: [hidden email]
Betreff: [Newbies] Does Set respect ordering?
 
Hi Folks.


If I have an OrderedCollection and convert it to Set via asSet, am I
guaranteed that the resulting Set contains elements in the same order as the
OrderedCollection?

Here is my problem.

I have an OrderedCollection with the same element in it twice. By same
element, I mean they are the same object.

*an OrderedCollection(
A
NESTED  TABLE CELL
 
B
A
NESTED  TABLE CELL

)
*

Above, the first and third elements are the same XMLElement. I now this
because if I inspect them and then change one, the other changes.

if I run asSet on the OrderedCollection, I get what I need:

*a Set( A
NESTED  TABLE CELL
 
B)*


In that conversion, can I rely on that Ordering being preserved?

If not, a pointer to the correct select/reject/inject/detect...sort of thing
would be much appreciated.

cheers.







--
Sent from: http://forum.world.st/Squeak-Beginners-f107673.html
_______________________________________________
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[hidden email]
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