So far I have only a monadic solution.
((?@+/){(;@((#~)</.]# ;@(i.@#)))@]) 5 3 4 2
On Fri, May 27, 2011 at 1:22 PM, Roger Hui <[email protected]> wrote:
> How is there favoritism?
>
> b=: 1 1
> (+/\b)%+/b
> 0.5 1
> +/0 1=/~0.5 1 I. 1e6 ?@$ 0
> 500380 499620
> +/0 1=/~0.5 1 I. 1e6 ?@$ 0
> 500866 499134
> +/0 1=/~0.5 1 I. 1e6 ?@$ 0
> 500429 499571
> +/0 1=/~0.5 1 I. 1e6 ?@$ 0
> 499958 500042
> +/0 1=/~0.5 1 I. 1e6 ?@$ 0
> 499918 500082
> +/0 1=/~0.5 1 I. 1e6 ?@$ 0
> 500454 499546
> +/0 1=/~0.5 1 I. 1e6 ?@$ 0
> 499724 500276
>
> The coin seems pretty fair to me.
>
>
>
> ----- Original Message -----
> From: Dan Bron <[email protected]>
> Date: Friday, May 27, 2011 10:08
> Subject: Re: [Jprogramming] Weighted random selection
> To: J Programming <[email protected]>
>
>> At first blush, that seems like it would favor higher indices
>> (right-er) over lower ones (left-er)?
>>
>> -Dan
>>
>> Please excuse typos; composed on a handheld device.
>>
>> -----Original Message-----
>> From: Roger Hui <[email protected]>
>> Sender: [email protected]
>> Date: Fri, 27 May 2011 09:50:06
>> To: Programming forum<[email protected]>
>> Reply-To: Programming forum <[email protected]>
>> Subject: Re: [Jprogramming] Weighted random selection
>>
>> Convert the weights to cumulative probabilities,
>> then use I. and ?0. Thus:
>>
>> Y=: 5 10 25 60
>> (+/\Y)%+/Y
>> 0.05 0.15 0.4 1
>> ((+/\Y)%+/Y) I. 20?@$ 0
>> 2 3 2 3 2 2 3 3 3 1 3 2 1 3 3 3 1 0 1 2
>>
>>
>>
>> ----- Original Message -----
>> From: Dan Bron <[email protected]>
>> Date: Friday, May 27, 2011 9:39
>> Subject: [Jprogramming] Weighted random selection
>> To: 'Programming forum' <[email protected]>
>>
>> > What's a clear, short verb to select random items in a
>> weighted
>> > fashion?Something like ? only:
>> >
>> > #0 Ranks 1 0 1
>> > #1 y=.vector of weights (proportional to their total)
>> > #2 x=.number of trials
>> > #3 the monad is the dyad with a fixed left arg of 1,
>> > i.e. 1&$: :
>> > ( ... )
>> > #4 result is x indexes into y (i.e. results e.
>> > i.#y) , selected
>> > at random, weighted by the index's proportion of the total
>> >
>> > Something like:
>> >
>> >
>> > require'stats numeric'
>> >
>> > wProb =: 1&$: :( discreterand@:(;~ ] ,:~ i.@# ) )"1 0 1
>> >
>> >
>> > ]
>> > results =. 4e5 wProb Y=.5 10 25 60
>> > 3 0 3 2 2 3 2 1 3 3 3 3 3 2 3 3 1 2 3 3 3 2 3 3 3 2 0 3
>> 3 3 3 3 3
>> > ...
>> > Y
>> > ,:~ (1 round 100 * #/.~ % #) (i.n=.#Y) , results
>> > 5 10 25 60
>> > 5 10 25
>> > 60
>> >
>> > Only discreterand seems a little heavyweight. Is there a
>> > simpler way?
>
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>
--
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Brian Schott
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