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From |
Joerg Luedicke <joerg.luedicke@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: create unique random number variable |

Date |
Tue, 24 Apr 2012 10:19:38 -0700 |

Stas, Just out of curiosity: could following this approach still be described as a strictly random draw (of course, 'strictly' in terms of pseudo-randomness) from a uniform distribution? Because what essentially happens is that the randomly emerging ties are filled in with yet another draw from the uniform. As a consequence, the resulting integers are drawn from a mixture of several or many uniform distributions. The component probabilities itself then depend on randomly emerging ties, so it should not make much different in practice. However, the resulting distribution looks somewhat smoother than one might expect (due to being a mixture of k uniforms, I presume). Compare the following histograms before and after the redraws (for which I modified your code): //draw from uniform (0,1) clear set obs 1000000 set seed 1234 generate uu =runiform() hist uu, name(unif, replace) bin(1000) //mapped to integers clear set obs 1000000 set seed 1234 generate uu = int(1500000*uniform()) bysort uu: generate byte nonuniq = _n > 1 hist uu, name(g0, replace) bin(1000) //drawing again in case of ties sum nonuniq while r(max) > 0 { bysort uu: replace uu = int(1500000*uniform()) if _n > 1 bysort uu: replace nonuniq = _n > 1 sum nonuniq, mean } hist uu, name(g1, replace) bin(1000) So I don't know what OP's demands are with regard to 'randomness', but maybe this could matter in some applications? (Perhaps in rocket science :) ) J. On Tue, Apr 24, 2012 at 7:43 AM, Stas Kolenikov <skolenik@gmail.com> wrote: > On Tue, Apr 24, 2012 at 4:37 AM, raoul reulen <r.c.reulen@gmail.com> wrote: >> Hello >> >> I'm trying to generate a random number variable like this: >> >> .set seed 12345 >> .gen x = int(1000*uniform()) >> >> However, the random numbers in variable x are not unique. Is there a >> way to ensure they are unique? > > clear > set obs 400 > * this is your sample size > > generate uu = int(1000*uniform()) > bysort uu: generate byte nonuniq = _n > 1 > sum nonuniq, mean > while r(max) > 0 { > bysort uu: replace uu = int(1000*uniform()) if _n > 1 > bysort uu: replace nonuniq = _n > 1 > sum nonuniq, mean > } > drop nonuniq > > -- > Stas Kolenikov, also found at http://stas.kolenikov.name > Small print: I use this email account for mailing lists only. > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: create unique random number variable***From:*Joerg Luedicke <joerg.luedicke@gmail.com>

**Re: st: create unique random number variable***From:*Stas Kolenikov <skolenik@gmail.com>

**References**:**st: create unique random number variable***From:*raoul reulen <r.c.reulen@gmail.com>

**Re: st: create unique random number variable***From:*Stas Kolenikov <skolenik@gmail.com>

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