A question about sets
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Hi there, i am new to Smalltalk and Pharo and today, while trying out some examples, i observed an somewhat strange behaviour. I used this snippet from the pharo.org website: | numbers | numbers := Set new. 10 timesRepeat: [ numbers add: 100 atRandom ]. numbers explore. Using Pharo 3.0 on my Laptop with Manjaro Linux 32bit and copy pasting the snippet above into the workspace i get sometimes a set with 10 values, sometimes with 9 values and once a set with just 8 values. Using this snippet, just to test the timesRepeat message: 10 timesRepeat: [ Transcript show: (100 atRandom); cr. ]. i always get 10 values. Is the behaviour with the first snippet correct? Giving sometimes 10 or 9 or even 8 values. Or is it a bug? I would expect to always get 10 values in my set. By the way i am totally excited about your cool programming environment. Keep on the good work. I justed started to explore it and can say it is awesome to work with. |
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Hi Fabian, Welcome on board ;-) Set: I represent a set of objects without duplicates. so if you have the same number multiple times, it cannot be added more than once in the Set.
replace Set by Bag (I represent an unordered collection of possibly duplicate elements.) and the size will always be 10. Best, Luc #Luc 2014-06-14 11:48 GMT+02:00 Fabian Boucsein <[hidden email]>:
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In reply to this post by Fabian Boucsein-2
In sets there can be only Unique nummers. So random produced a few of the same numbers. They get excluded from the set. Tim
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In reply to this post by Fabian Boucsein-2
Fabian Boucsein wrote:
Glad to hear you kind words. A Set is an unordered collection without duplicates, so adding the same number a second time does not increase the element count. The following code will make it obvious when you compare the number of duplicates in the Transcript with the contents of the Set. | numbers | numbers := Set new. 10 timesRepeat: [ | rand | rand := 100 atRandom. Transcript crShow: rand. numbers add: rand. ]. numbers explore. cheers -ben |
Re: A question about sets
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In reply to this post by Fabian Boucsein-2
Hi Fabien,
As other already explained, you just discovered the marvelous Set collection. Hilaire Le 14/06/2014 11:48, Fabian Boucsein a écrit : > i am new to Smalltalk and Pharo and today, while > trying out some examples, i observed an somewhat > strange behaviour. -- Dr. Geo http://drgeo.eu iStoa - https://launchpad.net/istoa |
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Hi Fabien and welcome, you just discovered this phenomenon: http://en.wikipedia.org/wiki/Birthday_problemOn Sun, Jun 15, 2014 at 12:12 AM, Hilaire Fernandes <[hidden email]> wrote: Hi Fabien, |
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About the birthday problem, I already pulished something that I had exeperimented in the classroom, but it is in French: http://irem.univ-reunion.fr/spip.php?article618 (clic on "problème des anniversaires" tab). The idea is that if you add say 30 times a "365 atRandom" to a bag (instead of a set) it happens now and then that a number appear more than once. In this classroom, two students actually had the same birthday, and they were eager to know of it happens often, so that they were very active for this exercise. Happy reading ;-)On Wed, Jun 25, 2014 at 12:10 PM, hilaire <[hidden email]> wrote: Alain, |
Re: A question about sets
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Great!
Now I wonder how it could be used within Dr. Geo. Thanks Hilaire Le 25/06/2014 18:33, Alain Busser a écrit : > About the birthday problem, I already pulished something that I had > exeperimented in the classroom, but it is in French: > http://irem.univ-reunion.fr/spip.php?article618 (clic on "problème des > anniversaires" tab). The idea is that if you add say 30 times a "365 > atRandom" to a bag (instead of a set) it happens now and then that a > number appear more than once. In this classroom, two students actually > had the same birthday, and they were eager to know of it happens often, > so that they were very active for this exercise. > > Happy reading ;-) > > Alain > > > On Wed, Jun 25, 2014 at 12:10 PM, hilaire > <[hidden email] > <mailto:[hidden email]>> wrote: > > Alain, > > I love very much your cultural insight and I would like to see more > examples > like this one applied to Dr. Geo scripting or Smalltalk sketches. > Personally, I don't have the time to both develop Dr. Geo *and* to > investigate such examples; contributions like yours are more than > welcome. > > Thanks > > Hilaire > > > > -- > View this message in context: > http://forum.world.st/A-question-about-sets-tp4763094p4764640.html > Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com. > > -- Dr. Geo http://drgeo.eu iStoa - https://launchpad.net/istoa |
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About the use of sets I found another idea: Eratosthene's sieve. Basically you create a set containing all integers from 2 to, say, 200.On Thu, Jun 26, 2014 at 8:21 PM, Hilaire Fernandes <[hidden email]> wrote: Great! |
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You're right but it should not have a fixed length because I want to remove numbers from it. I guess an SortedCollection is the best way to retrieve the next prime number. And the exercise is a good way to discover select and reject... Alain On Fri, Jun 27, 2014 at 1:41 PM, hilaire <[hidden email]> wrote: Why do you need a set for that? An array is enough. |
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In reply to this post by Alain Busser
Fun French Smalltalk. Il y a une version dispo? Phil Le 25 juin 2014 18:33, "Alain Busser" <[hidden email]> a écrit :
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btw I still plan to port it to Pharo3... AlainOn Sat, Jun 28, 2014 at 10:24 AM, [hidden email] <[hidden email]> wrote:
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