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Re: st: Re: select three non-identical random elements


From   Tomáš Houška <xbender@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Re: select three non-identical random elements
Date   Thu, 4 Apr 2013 14:38:28 +0200

Hi Joseph,

thank you for your tip! I was able to use that to solve my problem.
Tomas

2013/4/4 Joseph Coveney <stajc2@gmail.com>:
> Tomáš Houška wrote:
>
> I have list of items create by -levelsof- macro and I would like to select
> three items from that list at random and for them to be non-repetitive
> (i.e. each one can appear only once in the selection).
>
> Lets say I have a list -local list "one two three four five six"- and I
> would like to get
> local random1 =
> local random2 =
> local random3 =
>
> where each one is a random selection from the local list and each item
> appears at max once.
> I would appreciate any help on how to do that.
>
> --------------------------------------------------------------------------------
>
> Macro extended functions for manipulating lists (-help macrolists-) will help
> you to randomly sample without replacement from a local macro containing a list
> of words.
>
> As Nick mentions, there might be better ways in the long run using Mata, but
> this should get you going until then.
>
> Joseph Coveney
>
> .
> . local word_list one two three four five six
>
> .
> . local want 3
>
> .
> . set seed `=date("2013-04-03", "YMD")'
>
> .
> . local words : word count `word_list'
>
> . assert `want' <= `words'
>
> .
> . local loop 1
>
> . while `loop' <= `want' {
>   2.         local randu = 1 + floor((`words' - 1) * runiform())
>   3.         local random`loop' : word `randu' of `word_list'
>   4.         local word_list : list word_list - random`loop'
>   5.         local --words
>   6.         local ++loop
>   7. }
>
> .
> . display "`random1'"
> five
>
> . display "`random2'"
> one
>
> . display "`random3'"
> four
>
>
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