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Re: Random choice

  • To: mathgroup at smc.vnet.net
  • Subject: [mg99839] Re: Random choice
  • From: "Steve Luttrell" <steve at _removemefirst_luttrell.org.uk>
  • Date: Fri, 15 May 2009 06:26:26 -0400 (EDT)
  • References: <guj8ef$hv6$1@smc.vnet.net>

You need to do sampling without replacement. This code fragment will sample 
m times (without replacement) from a pool of n indices:

n;
m=5;
Nest[({Append[#1[[1]],#1[[2,#2]]],Delete[#1[[2]],#2]}&[#,RandomInteger[{1,Length[#[[2]]]}]])&,{{},Range[n]},m]

{{12,6,13,14,8},{1,2,3,4,5,7,9,10,11,15,16,17,18,19,20}}

The code returns 2 lists: the sampled indices and the residue of the pool 
which was sampled from. This output can be fed back into the code fragment 
for further sampling if required.

-- 
Stephen Luttrell
West Malvern, UK

"Valeri Astanoff" <astanoff at gmail.com> wrote in message 
news:guj8ef$hv6$1 at smc.vnet.net...
> Good day,
>
> Given this example :
>
> In[1]:= RandomChoice[Range[500], 100] // Union // Length
>
> Out[1]= 91
>
> what is the best way to get *exactly* 100 different
> random numbers ranging from 1 to 500 ?
>
> Any piece of advice would be appreciated.
>
> --
>
> Valeri Astanoff
> 



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