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 > > > > > > > > > > > >
