This is exactly how I think and feel about bags. Thanks Richard.
Am .03.2019, 01:35 Uhr, schrieb Richard O'Keefe <rao...@gmail.com>:
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 <s...@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 <s...@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 >> >> >
