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Re: need help

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87357] Re: need help
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Tue, 8 Apr 2008 07:15:53 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <ftcoug$ksr$1@smc.vnet.net>

haitomi wrote:

> I need help with two pure functions
> 
> 1)  Li[Ranlist,x] that return a list of x element selected at random from Ranlist.  (Is there any way to gennerate random from Ranlist? For example I have RanList=Range[-100,100])

<snip>

Hi Tomi,

I am not sure to have understood what you are looking for, but I hope 
the following will help.

First, note that if one wants to get a list of, say ten, integers within 
the range [-100, 100], one can use RandomInteger as in

     RandomInteger[{-100, 100}, 10]

     {-60, -36, -40, -45, 6, 26, -84, 2, -45, 77}

There exists some other functions such as RandomReal or RandomComplex 
too. If one wants to randomly pick out some symbols, one can use

     RandomChoice[{a, b, c}, 10]

     {c, a, b, b, c, c, c, b, b, c}

Now if you prefer to write your own function, you could use something 
like the following:

     f1[lst_, n_?NonNegative] /; n <= Length[lst] :=
         lst[[RandomInteger[{1, Length[lst]}, n]]]

     RanList = Range[-10, 10]

     {-10,-9,-8,-7,-6,-5,-4,-3,-2,-1,0,1,2,3,4,5,6,7,8,9,10}

     (* We randomly pick out five integer values out of twenty. *)

     f1[RanList, 5]

     {-3, 7, -3, 9, 1}


Regards,
-- Jean-Marc


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