In my opinion, having sum and sum: aBlock is a good point. The only problem to solve is to have an elegant solution working even if it's an empty collection. I think the solution proposed by Doru is really satisfying.
2013/4/22 Nicolas Cellier <nicolas.cellier.aka.n...@gmail.com> > Or maybe sumEach: #squared... Anyway, current Squeak #detectSum: sounds > awful, so it shouldn't be hard to find a better name > > > 2013/4/22 Nicolas Cellier <nicolas.cellier.aka.n...@gmail.com> > >> Personnally, I like #sumOf:, like for example (1 to: 10) sumOf: #squared. >> Same with maxOf: minOf: productOf: ... >> >> >> 2013/4/22 Frank Shearar <frank.shea...@gmail.com> >> >>> On 22 April 2013 12:32, Sven Van Caekenberghe <s...@stfx.eu> wrote: >>> > Hi, >>> > >>> > I agree with Frank on the processing block: it has nothing to do with >>> summing. >>> > >>> > Mathematically, defining adding (sum) leads to a neutral element >>> (zero). But you only need it if the collection is empty. >>> > >>> > The trick of the #zero selector is elegant, but not needed with the >>> #anyOne trick. >>> >>> That's a good point. I thought of #zero because my own hacking on >>> SqueakCheck led naturally to thinking of protocols: using a class-side >>> #zero means that I could work with "all objects that understand + and >>> have a zero". >>> >>> #collectAndSum: might be a good name for the method, actually. >>> >>> frank >>> >>> > Currently, #sum does not work with empty collections in Pharo, which >>> surprised me. >>> > >>> > I would add a >>> > >>> > Collection>>#sumFrom: value >>> > ^ self inject: value into: [ :sum :each | sum + each ] >>> > >>> > And change >>> > >>> > Collection>>#sum >>> > | sample sum | >>> > self isEmpty ifTrue: [ ^ self sumFrom: 0 ]. >>> > sample := self anyOne. >>> > sum := self inject: sample into: [ :sum :each | sum + each ]. >>> > ^ sum - sample >>> > >>> > A variant with an additional collect style processing block could be >>> added along these lines, #sum: and #sum:from: >>> > >>> > Sven >>> > >>> > On 22 Apr 2013, at 12:29, Frank Shearar <frank.shea...@gmail.com> >>> wrote: >>> > >>> >> "Sum" is usually well-defined, so I don't understand what the block's >>> >> for. With the block it's more like "take this collection, map the >>> >> values with some function, and sum the result". >>> >> >>> >> If so, it sounds like you're looking for a sugared form of >>> >> (myCollection collect: aBlock) inject: self first class zero into: #+. >>> >> ? >>> >> >>> >> (There's already Float class >> #zero and (in Squeak at least) Integer >>> >> class >> #zero, and so on. Just add MyUnit class >> #zero and you're >>> >> done.) >>> >> >>> >> frank >>> >> >>> >> On 22 April 2013 10:37, Tudor Girba <tu...@tudorgirba.com> wrote: >>> >>> Hi, >>> >>> >>> >>> I am CC-ing the pharo mailing list because it can be of interest. >>> >>> >>> >>> I agree with Guillaume that there is a legitimate need for a generic >>> >>> solution. However, at the same time we lose the convenience of >>> simply adding >>> >>> numbers, which is likely to be the most encountered use case. >>> >>> >>> >>> I see a couple of possibilities: >>> >>> - add Collection>>sum: aBlock from: aZeroValue that takes aZeroValue >>> as the >>> >>> default. >>> >>> - add Collection>>sumNumbers: aBlock that takes 0 as default rather >>> than >>> >>> anyOne. >>> >>> >>> >>> What do you think? >>> >>> >>> >>> Cheers, >>> >>> Doru >>> >>> >>> >>> >>> >>> >>> >>> On Mon, Apr 22, 2013 at 10:14 AM, Guillaume Larcheveque >>> >>> <guillaume.larcheve...@gmail.com> wrote: >>> >>>> >>> >>>> For example, in Artefact we use Units and I have tried to use sum >>> but it >>> >>>> doesn't works because Units doesn't allow to do 0 + 4 cm which is >>> >>>> inconsistent. >>> >>>> >>> >>>> >>> >>>> 2013/4/22 Alexandre Bergel <alexandre.ber...@me.com> >>> >>>>> >>> >>>>> Thanks for letting us know. I cannot see a case where having 0 as >>> the >>> >>>>> initial value does not work as expected. >>> >>>>> >>> >>>>> Cheers, >>> >>>>> Alexandre >>> >>>>> >>> >>>>> >>> >>>>> Le 21 avr. 2013 à 17:35, Tudor Girba <tu...@tudorgirba.com> a >>> écrit : >>> >>>>> >>> >>>>>> Hi, >>> >>>>>> >>> >>>>>> Pharo 2.0 comes with Collection>>sum: >>> >>>>>> >>> >>>>>> Collection>>sum: aBlock >>> >>>>>> "This is implemented using a variant of the normal inject:into: >>> >>>>>> pattern. >>> >>>>>> The reason for this is that it is not known whether we're in the >>> >>>>>> normal >>> >>>>>> number line, i.e. whether 0 is a good initial value for the sum. >>> >>>>>> Consider a collection of measurement objects, 0 would be the >>> >>>>>> unitless >>> >>>>>> value and would not be appropriate to add with the unit-ed >>> objects." >>> >>>>>> | sum sample | >>> >>>>>> sample := aBlock value: self anyOne. >>> >>>>>> sum := self inject: sample into: [ :previousValue :each | >>> >>>>>> previousValue + (aBlock value: each) ]. >>> >>>>>> ^ sum - sample >>> >>>>>> >>> >>>>>> To some extent, this is more generic than the one we had in Moose >>> that >>> >>>>>> considered only numbers: >>> >>>>>> Collection>>sum: aSymbolOrBlock >>> >>>>>> ^ self >>> >>>>>> inject: 0 >>> >>>>>> into: [:sum :each | sum + (aSymbolOrBlock value: each)] >>> >>>>>> >>> >>>>>> >>> >>>>>> However, with the Pharo 2.0 implementation the collection must >>> not be >>> >>>>>> empty, while the other implementation we get 0. If the collection >>> is empty, >>> >>>>>> you get an exception due to anyOne. >>> >>>>>> >>> >>>>>> This induced several errors in metric computations (like number of >>> >>>>>> methods of a package when the package had no classes). These are >>> now fixed, >>> >>>>>> but I thought I would let you know just in case you want to rely >>> on this >>> >>>>>> method. >>> >>>>>> >>> >>>>>> I actually still believe we would benefit from a robust but more >>> >>>>>> limited sum:. Perhaps we could have sumNumbers:. >>> >>>>>> >>> >>>>>> Cheers, >>> >>>>>> Doru >>> >>>>>> >>> >>>>>> >>> >>>>>> -- >>> >>>>>> www.tudorgirba.com >>> >>>>>> >>> >>>>>> "If you can't say why something is relevant, >>> >>>>>> it probably isn't." >>> >>>>>> >>> >>>>>> >>> >>>>>> _______________________________________________ >>> >>>>>> Moose-dev mailing list >>> >>>>>> moose-...@iam.unibe.ch >>> >>>>>> https://www.iam.unibe.ch/mailman/listinfo/moose-dev >>> >>>>> >>> >>>>> _______________________________________________ >>> >>>>> Moose-dev mailing list >>> >>>>> moose-...@iam.unibe.ch >>> >>>>> https://www.iam.unibe.ch/mailman/listinfo/moose-dev >>> >>>> >>> >>>> >>> >>>> -- >>> >>>> Guillaume Larcheveque >>> >>>> >>> >>>> _______________________________________________ >>> >>>> Moose-dev mailing list >>> >>>> moose-...@iam.unibe.ch >>> >>>> https://www.iam.unibe.ch/mailman/listinfo/moose-dev >>> >>> >>> >>> -- >>> >>> www.tudorgirba.com >>> >>> >>> >>> "Every thing has its own flow" >>> > >>> > >>> > -- >>> > Sven Van Caekenberghe >>> > Proudly supporting Pharo >>> > http://pharo.org >>> > http://association.pharo.org >>> > http://consortium.pharo.org >>> > >>> > >>> > >>> > >>> > >>> >>> >> > -- *Guillaume Larcheveque*
