[Pharo-users] Why can't a Bag answer as a dictionary?

[Tim Mackinnon]

I was surprised to find that a Bag can’t convert to a dictionary - e.g.

Bag new 
addAll: 'aacddd’; 
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

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[Sven Van Caekenberghe]

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: 'ABABAB'; valuesAndCounts.

> On 6 Mar 2019, at 14:25, Tim Mackinnon  wrote:
> 
> I was surprised to find that a Bag can’t convert to a dictionary - e.g.
> 
> Bag new 
>   addAll: 'aacddd’; 
>   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

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[Richard O'Keefe]

Doubtless the original poster expected aBag asDictionary
to answer a dictionary mapping the (distinct) elements of
the bag to their counts.  Mathematically, a bag can
usefully be seen as a partial function from a set U to
the positive integers, and a dictionary with U keys and
positive integer values is precisely that.

It's really not unreasonable to expect that,
considering that there *is* a method that does just
what the OP wanted: #valuesAndCounts.  It's rather
dangerous to expose private state like that, but it
is not a private method.  I would expect

asDictionary
  ^contents copy




On Thu, 7 Mar 2019 at 02:54, Sven Van Caekenberghe  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: 'ABABAB'; valuesAndCounts.
>
> > On 6 Mar 2019, at 14:25, Tim Mackinnon  wrote:
> >
> > I was surprised to find that a Bag can’t convert to a dictionary - e.g.
> >
> > Bag new
> >   addAll: 'aacddd’;
> >   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
>
>
>

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[Tim Mackinnon]

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.




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  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: 'ABABAB'; valuesAndCounts.
> 
>> On 6 Mar 2019, at 14:25, Tim Mackinnon  wrote:
>> 
>> I was surprised to find that a Bag can’t convert to a dictionary - e.g.
>> 
>> Bag new 
>>  addAll: 'aacddd’; 
>>  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
> 
> 

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[Sven Van Caekenberghe]

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  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.
> 
> 
> 
> 
> 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  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: 'ABABAB'; valuesAndCounts.
>> 
>>> On 6 Mar 2019, at 14:25, Tim Mackinnon  wrote:
>>> 
>>> I was surprised to find that a Bag can’t convert to a dictionary - e.g.
>>> 
>>> Bag new 
>>> addAll: 'aacddd’; 
>>> 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
>> 
>> 
> 

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[p...@highoctane.be]

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  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  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.
> >
> > 
> >
> >
> > 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  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: 'ABABAB'; valuesAndCounts.
> >>
> >>> On 6 Mar 2019, at 14:25, Tim Mackinnon  wrote:
> >>>
> >>> I was surprised to find that a Bag can’t convert to a dictionary - e.g.
> >>>
> >>> Bag new
> >>> addAll: 'aacddd’;
> >>> 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
> >>
> >>
> >
>
>
>
>

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[Tim Mackinnon]

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

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, p...@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  > 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  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.
> > 
> > 
> > 
> > 
> > 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  >> > 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: 'ABABAB'; valuesAndCounts.
> >> 
> >>> On 6 Mar 2019, at 14:25, Tim Mackinnon  wrote:
> >>> 
> >>> I was surprised to find that a Bag can’t convert to a dictionary - e.g.
> >>> 
> >>> Bag new 
> >>> addAll: 'aacddd’; 
> >>> 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
> >> 
> >> 
> > 
> 
> 
> 

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[Sven Van Caekenberghe]

I am still not convinced.

> On 6 Mar 2019, at 19:24, Tim Mackinnon  wrote:
> 
> I still am tempted to make asDictionary work - because the the moment you get 
> a #key , DNU error - which is definitely not right.

The error might not be super clear, but it is not wrong, the elements of your 
collection do not respond to #key, a necessity to create a dictionary from a 
collection of associations/pairs.

Also, if you modify #asDictionary like that, then

   as: #Dictionary 

will still fail.

This is all not so simple as it seems.

> 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, p...@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  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  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.
>> > 
>> > 
>> > 
>> > 
>> > 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  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: 'ABABAB'; valuesAndCounts.
>> >> 
>> >>> On 6 Mar 2019, at 14:25, Tim Mackinnon  wrote:
>> >>> 
>> >>> I was surprised to find that a Bag can’t convert to a dictionary - e.g.
>> >>> 
>> >>> Bag new 
>> >>> addAll: 'aacddd’; 
>> >>> 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
>> >> 
>> >> 
>> > 
>> 
>> 
>> 
> 

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[Richard Sargent]

On Wed, Mar 6, 2019 at 10:25 AM Tim Mackinnon  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, p...@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  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  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.
>> >
>> > 
>> >
>> >
>> > 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  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: 'ABABAB'; valuesAndCounts.
>> >>
>> >>> On 6 Mar 2019, at 14:25, Tim Mackinnon  wrote:
>> >>>
>> >>> I was surprised to find that a Bag can’t convert to a dictionary -
>> e.g.
>> >>>
>> >>> Bag new
>> >>> addAll: 'aacddd’;
>> >>> 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
>> >>
>> >>
>> >
>>
>>
>>
>>
>

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[Richard O'Keefe]

To me, a bag is first and foremost a multiset.
Yes, it's a collection, but it's not *just* a collection.
It's a very specific kind of collection with a very
salient "characteristic function".

In my own Smalltalk library, #asDictionary isn't even *defined*
on things that are not dictionaries or some kind of mapping,
because let's face it, a dictionary *isn't* a collection of
Associations, and trying to make it look like one made
Smalltalk-80 rather inconsistent.  For example, if a dictionary
were a collection of associations, you would expect
(Dictionary with: #a -> 1 with: #b -> 2) includes: #a -> 1
to be true. No, it's false.  You would expect
(Dictionary with: #a -> 1 with: #b -> 2) asArray
to be (a->1 b->2).  No, it's (1 2).  In order to avoid major
confusion, I had to learn never to think of Associations in
connection with Dictionaries.  So I expect #asDictionary to
have something to do with #keysAndValuesDo:.
or something like that.

For {1->2. 3->4} asDictionary I would have to write
Dictionary withAllAssociations: {1->2. 3->4}
except that I never actually found a use for it.

#valuesAndCounts is a method that violates good OO practice,
because it exposes (what you'd expect to be) private state.
For example,
  b := 'abracadabra' asBag.
  b valuesAndCounts at: $a put: 'BOOM!'.
  b
select, Print It, BOOM!.  It should *copy* the dictionary.



On Thu, 7 Mar 2019 at 04:50, Sven Van Caekenberghe  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  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.
> >
> > 
> >
> >
> > 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  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: 'ABABAB'; valuesAndCounts.
> >>
> >>> On 6 Mar 2019, at 14:25, Tim Mackinnon  wrote:
> >>>
> >>> I was surprised to find that a Bag can’t convert to a dictionary - e.g.
> >>>
> >>> Bag new
> >>> addAll: 'aacddd’;
> >>> 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
> >>
> >>
> >
>
>
>

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[Richard O'Keefe]

Handlingas: Dictionary
is really quite straightforward.
Add a one-line method to Bag:

Bag>>
associationsDo: aBlock
contents associationsDo: aBlock.

This is a good idea anyway, because currently there is a bug where
aBag associationsDo: aBlock
fails to pass Associations to aBlock.  Once you have done that,
'abracadabra' asBag as: Dictionary
just works.  This one simple addition
 - makes aBag associationsDo: aBlock work when it didn't before
 - makes aBag asDictionary work
 - makes aBag as: Dictionary work
 - makes Dictionary newFrom: aBag work




On Thu, 7 Mar 2019 at 07:35, Sven Van Caekenberghe  wrote:

> I am still not convinced.
>
> > On 6 Mar 2019, at 19:24, Tim Mackinnon  wrote:
> >
> > I still am tempted to make asDictionary work - because the the moment
> you get a #key , DNU error - which is definitely not right.
>
> The error might not be super clear, but it is not wrong, the elements of
> your collection do not respond to #key, a necessity to create a dictionary
> from a collection of associations/pairs.
>
> Also, if you modify #asDictionary like that, then
>
>as: #Dictionary
>
> will still fail.
>
> This is all not so simple as it seems.
>
> > 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, p...@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 
> 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  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.
> >> >
> >> > 
> >> >
> >> >
> >> > 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  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: 'ABABAB'; valuesAndCounts.
> >> >>
> >> >>> On 6 Mar 2019, at 14:25, Tim Mackinnon  wrote:
> >> >>>
> >> >>> I was surprised to find that a Bag can’t convert to a dictionary -
> e.g.
> >> >>>
> >> >>> Bag new
> >> >>> addAll: 'aacddd’;
> >> >>> 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
> >> >>
> >> >>
> >> >
> >>
> >>
> >>
> >
>
>
>

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[Steffen Märcker]

This is exactly how I think and feel about bags. Thanks Richard.

Am .03.2019, 01:35 Uhr, schrieb Richard O'Keefe :


To me, a bag is first and foremost a multiset.
Yes, it's a collection, but it's not *just* a collection.
It's a very specific kind of collection with a very
salient "characteristic function".

In my own Smalltalk library, #asDictionary isn't even *defined*
on things that are not dictionaries or some kind of mapping,
because let's face it, a dictionary *isn't* a collection of
Associations, and trying to make it look like one made
Smalltalk-80 rather inconsistent.  For example, if a dictionary
were a collection of associations, you would expect
(Dictionary with: #a -> 1 with: #b -> 2) includes: #a -> 1
to be true. No, it's false.  You would expect
(Dictionary with: #a -> 1 with: #b -> 2) asArray
to be (a->1 b->2).  No, it's (1 2).  In order to avoid major
confusion, I had to learn never to think of Associations in
connection with Dictionaries.  So I expect #asDictionary to
have something to do with #keysAndValuesDo:.
or something like that.

For {1->2. 3->4} asDictionary I would have to write
Dictionary withAllAssociations: {1->2. 3->4}
except that I never actually found a use for it.

#valuesAndCounts is a method that violates good OO practice,
because it exposes (what you'd expect to be) private state.
For example,
  b := 'abracadabra' asBag.
  b valuesAndCounts at: $a put: 'BOOM!'.
  b
select, Print It, BOOM!.  It should *copy* the dictionary.



On Thu, 7 Mar 2019 at 04:50, Sven Van Caekenberghe  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  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.
>
> 
>
>
> 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  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: 'ABABAB'; valuesAndCounts.
>>
>>> On 6 Mar 2019, at 14:25, Tim Mackinnon  wrote:
>>>
>>> I was surprised to find that a Bag can’t convert to a dictionary -
e.g.
>>>
>>> Bag new
>>> addAll: 'aacddd’;
>>> 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
>>
>>
>

Re: [Pharo-users] Why can't a Bag answer as a dictionary?

[Cédrick Béler]

> 
>  #(1 2 3) asDictionary 
> 


For this one,  I would expect a dictionary with integer keys
I see a dictionary as an indexed collection with key that are not only integer 
(like for an array).


1->1 2->2 3->3



I doubt this would be useful though.

My 2 cents,

Cédrick