Re: [Pharo-users] [pharo-project/pharo] Proposed improvement : performance of #atRandom: in class Bag (#5392)

[Benoit St-Jean via Pharo-users]

--- Begin Message --- While I'm at it, another improvement would be to buffer #newFrom: by reading large chunks of the argument <aCollection> via a ReadStream, adding the objects read to a <Bag> buffer and inserting into the receiver via #add:withOccurrences:.  That way, if you read say 1000 object (of which lots are similar), you don't have to "add" 1000 items, you could reduce the number of adds by reducing the duplicates with this buffer bag.  Wouldn't make much of a difference in the worst case scenario but one can assume that since you're using a bag, you normally expect a lot of dups!  So we could gain a lot that way.  Anyway, that's what I'm seeing with my experiments (millions of objects) and I'm still contemplating that improvement with more & more tests (such as adjusting the buffer size).  So far, this is really promising!

On 2019-12-18 06:32, Sven Van Caekenberghe wrote:

OK, now I see. I was thrown off by the weird formatting ;-)

The final expression is not needed, since you started with an emptyCheck.

Reformatted then:

|Bag>>#atRandom: aGenerator "Answer a random element of the receiver. Uses aGenerator which should be kept by the user in a variable and used every time. Use this instead of #atRandom for better uniformity of random numbers because only you use the generator. Causes an error if self has no elements." | rand index | self emptyCheck. rand := aGenerator nextInt: self size. index := 0. self doWithOccurrences: [ :key :count | index := index + count. rand <= index ifTrue: [ ^ key ] ] |

Still, we need a PR as well. And maybe a specific test unless this is already covered by other tests.

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