On Wed, Mar 6, 2019 at 10:25 AM Tim Mackinnon <tim@testit.works> wrote:

I still am tempted to make asDictionary work - because the the moment you get a #key , DNU error - which is definitely not right.

This argument gives me the willies. Sorry.

I can see an argument that a sequenceable collection can implement a meaningful #asDictionary, using #keysAndValuesDo:. The key is the index of each element, so it makes sense.

But, #asDictionary for a non-sequenceable collection doesn't make sense (other than for Dictionary and its variants, obviously). What would the keys be from a Set, for example?

Bag>>#asDictionary makes sense if (and in my opinion, only if) you define it to rely on the internal implementation. #valuesAndCounts make sense because it doesn't rely on internal implementation details to define it, although it typically is implemented to use those internal implementation details. I think expressing it as a conversion is a poor choice. Asking it for a different representation is good.

[And as an aside, given that the API expresses #occurrencesOf:, #valuesAndCounts might have been better named #valuesAndOccurrences (and perhaps "With" rather than "And").]

So should Bag asDictionary give you a reasonable dictionary, or should it throw a proper exception - something like:

DomainError signal: ��#asDictionary not supported, use #valueAndCounts��

Is that better - or do we accept that it inherits it from Collection and so can do something useful?

Tim

On 6 Mar 2019, at 18:11, phil@highoctane.be wrote:

And when asking the object:

#(1 2 4 5 6 7 2 1 4 3) asBag�� isDictionary

we get false. So, not, not a dictionary.

I still have been using #valuesAndCounts to get the dictionary out of a bag on several occasions.

And is useful indeed.

#(1 2 4 5 6 7 2 1 4 3) asBag occurrencesOf: 2

and��

#(1 2 4 5 6 7 2 1 4 3) asBag valuesAndCounts at: 2��

seem pretty much the same.

But in this age of streams/reactive streams and lazy evaluations, what do we have in Pharo on that front?

Phil

On Wed, Mar 6, 2019 at 4:49 PM Sven Van Caekenberghe <sven@stfx.eu> wrote:
I was just explaining how it is now, what I think the rationale is behind it.

I understand #asDictionary as working on a collection of pairs/associations (because it basically goes to #withAll:).

A bag is just a collection that is optimised for many duplicates, the fact that you have values and counts is more an implementation detail than an intrinsic property.

The conversion that you want, and that already exists in #valuesAndCounts is one interpretation of what a bag is, not the only one. A bag is foremost a collection of things.

I am not immediately convinced that #valuesAndCounts should be the default #asDictionary interpretation.

What about the inverse for example ?

�� { #foo->2. #bar->3 } asDictionary asBag.

But this is certainly an interesting discussion.

> On 6 Mar 2019, at 16:23, Tim Mackinnon <tim@testit.works> wrote:
>
> As Richard said - as a bag is relationship between keys and frequencies, I would expect it to be able to convert to a dictionary.
>
> It displays in an inspector just like a Dictionary - which is why I figured I could convert to pass it back to the exercise that was written with Dictionaries in mind.
>
> <PastedGraphic-3.png>
>
>
> The code to fix it is quite simple, but on these kinds of things - I thought it worth checking before submitting a PR.
>
> Tim
>
>
>> On 6 Mar 2019, at 13:53, Sven Van Caekenberghe <sven@stfx.eu> wrote:
>>
>> Why would that work ? What would you expect the output to be ?
>>
>> Try:
>>
>>�� #(1 2 3) asDictionary
>>
>> it fails in exactly the same way. You need key/value pairs (Associations).
>>
>> These do work
>>
>>�� Bag new add: #foo->100; asDictionary.
>>
>>�� Bag new addAll: 'ABABABAAAA'; valuesAndCounts.
>>
>>> On 6 Mar 2019, at 14:25, Tim Mackinnon <tim@testit.works> wrote:
>>>
>>> I was surprised to find that a Bag can��t convert to a dictionary - e.g.
>>>
>>> Bag new
>>>�� addAll: 'aabbbbcddd��;
>>>�� asDictionary
>>>
>>> Gives an error - Dnu #key
>>>
>>>
>>> It looks to me like Bag is inheriting a bad version of #associationsDo:�� and instead could simply forward it to #doWithOccurences: instead?
>>>
>>> I know Bag is not used that much - but it comes up a lot in programming exercises.
>>>
>>> Tim
>>
>>
>