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From: Ted Dunning <ted.dunning@gmail.com>
Date: Mon, 11 Mar 2013 16:53:48 -0700
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 <CAJwFCa2uDoL8PzFqp+ijai0QpebQ3OnRMWTqy5vz1maqdVtmVg@mail.gmail.com>
Subject: Re: [Bag] random pick
To: Commons Developers List <dev@commons.apache.org>
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Othmen,

The common way to contribute code is to file a bug report/enhancement
request at the correct commons component:

https://issues.apache.org/jira/secure/BrowseProjects.jspa#10260

My guess is that you want collections which is at

https://issues.apache.org/jira/browse/COLLECTIONS

Then you should put your suggested solution onto that JIRA as an
attachment.  The attachment should be a patch file.  That will be a place
that the merits of the contribution can be discussed.

My own comment here is that the common idiom in the English statistical
literature for sampling from a bag is either sampling without replacement
or sampling with replacement.  Moreover, it is typical that you allow for
multiple items to be sampled rather than requiring sampling to proceed one
element at a time.  Sampling n items from an n-item bag without
replacement, for instance, would return a permutation of the bag (if you
get an ordered sample) or a partition of the bag (if you get an unordered
sample).

There is also the question of whether the bag should be considered
immutable during sampling.  If you want to leave the bag unchanged by
sampling, then you probably should be returning a sampler object of some
kind that is kind of a randomized iterator or iterable.

These kinds of design decisions need to be hashed out in the process of
getting your contribution into the code.


Good luck with your contribution!

On Mon, Mar 11, 2013 at 4:16 PM, Othmen Tiliouine <
tiliouine.othmen@gmail.com> wrote:

> Hello,
>
> I just saw the Bag interface and its implementations, I'm surprised that
> Bag
> <T> (and none of these implementations) expose the method
> public T pick() and public T pickAndRemit() (pick a random element)
> The Bag object we see in nature, it is mainly used to this, that's why
> it is widely
> used in the probability that when I met 2 white balls and one black, when I
> draw a ball randomly I have 2 times more likely to have a white ball
>
> I think that if this caracteristic exists it would be very valuable.
>
>
> this is a simple implementation of pick() and pickAndRemit() with HashBag
>
> package com.otiliouine.commons.collections;
>
> import java.util.Iterator;
>
> import org.apache.commons.collections.bag.HashBag;
>
> public class OpaqueHashBag extends HashBag implements OpaqueBag {
>
>     public Object pcik() {
>         if (size() == 0) {
>             return null;
>         }
>         int randomIndex = (int) (Math.random() * size());
>         int searchIndex = randomIndex;
>
>         Iterator iterator = this.iterator();
>         //iterator = this.map.keySet().iterator()
>         Object selectedItem = iterator.next();
>         int count;
>
>         while (searchIndex > 0) {
>             searchIndex --;
>             selectedItem = iterator.next();
>         }
> //        while ((count = getCount(selectedItem)) < searchIndex + 1) {
> //            searchIndex -= count;
> //            selectedItem = iterator.next();
> //        }
>         return selectedItem;
>     }
>
>     public Object pickAndRemit() {
>         Object picked = pcik();
>         if (picked != null) {
>             remove(picked, 1);
>         }
>         return picked;
>     }
> }
>
>
>
> it can be optimized if it is writen in AbstractMapBag class
>
> and this is the test
>
> public class TestOpaqueHashBag {
>
>     private OpaqueHashBag bag;
>
>     public static void main(String ... args) {
>         TestOpaqueHashBag t = new TestOpaqueHashBag();
>         t.before();
>         t.testpick();
>     }
>
>     public void before(){
>         bag = new OpaqueHashBag();
>         bag.add("white", 6);
>         bag.add("black", 3);
>         bag.add("red", 1);
>     }
>
>     public void testpick() {
>         int w = 0, b = 0, r = 0;
>         for (int i = 0; i < 1000; i++) {
>             String ball = (String) bag.pcik();
>
>             if (ball.equals("white")) {
>                 w ++;
>             } else if (ball.equals("black")) {
>                 b ++;
>             } else {
>                 r ++;
>             }
>         }
>         System.out.println("%white = " + w/10);
>         System.out.println("%black = " + b/10);
>         System.out.println("%red = " + r/10);
>     }
>
> }
>
> output :
>
> %white = 59
> %black = 30
> %red = 9
>
>
> Othmen TILIOUINE
>

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