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From |
Michael McCulloch <mm@pinestreetfoundation.org> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: generating random numbers without replacement |

Date |
Fri, 24 May 2013 22:23:02 -0700 |

Thank you kindly Nick for the translation! How would I rewrite the ultimate line (a, meaning "now show me a), to instead generate the variable a according to the preceding specifications? And, can you recommend a book or tutorial that explains Mata as you so clearly do here? Best wishes, Michael McCulloch, LAc MPH PhD -- Pine Street Foundation, since 1989 124 Pine Street | San Anselmo | California | 94960-2674 P: (415) 407-1357 | F: (206) 338-2391 | http://www.PineStreetFoundation.org On May 24, 2013, at 10:05 PM, Nick Cox wrote: > Note that the Mata code misses a trick > > a = J(100,1,.) > for(i = 1; i<=100; i++) a[i,1] = i > > is a long-winded alternative to > > a = 1::100 > > In fact you could shorten the code further, but I will stop there. > > One Stata translation is > > set obs 100 > gen a = _n > gen rnd = runiform() > sort rnd > l a rnd > > I would usually preface that by -set seed 2803- or some such. > > Here is a line-by-line translation > > mata > // open Mata > a=J(100,1,.) > // a is a vector with 100 rows, 1 column, all missing values > for(i=1;i<=100;i++) a[i,1]=i > // loop from i = 1 to i = 100 incrementing i by 1 at each step: > // set the i th row and 1st column of a to i > a=a,runiform(100,1) > // join a row-by-row with a vector with 100 rows, 1 column of uniform > random numbers > a=sort(a,2) > // sort a according to the values in the second column: > // wanted consequence is a random shuffle of 1::100 in first column > a > // now show me a > > I wrote -swor- a while back, but I can't remember much about it. More > important is -sample-. > > SJ-5-1 dm86_1 . . . . . . . . . . . . . . . . . . . Software update for swor > (help swor if installed) . . . . . . . . . . . . . . . . . N. J. Cox > Q1/05 SJ 5(1):139 > swor rewritten to use sort, stable for reproducibility and > sortpreserve for compatibility; help file also modernized > > STB-59 dm86 Sampling without replacement: abs. sample sizes & keeping all obs > (help swor if installed) . . . . . . . . . . . . . . . . . N. J. Cox > 1/01 pp.8--9; STB Reprints Vol 10, pp.38--39 > samples without replacement a specified sample size; > alternative to sample > > Nick > njcoxstata@gmail.com > > On 24 May 2013 22:30, Michael McCulloch <mm@pinestreetfoundation.org> wrote: > >> I wish to generate random numbers between 1 and 5, without replacement. I have located the following Mata code, but have not yet learned Mata. Is it possible to rewrite this to create the variable a? >> >> mata >> a=J(100,1,.) >> for(i=1;i<=100;i++) a[i,1]=i >> a=a,runiform(100,1) >> a=sort(a,2) >> a >> end >> > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/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/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: generating random numbers without replacement***From:*Nick Cox <njcoxstata@gmail.com>

**References**:**st: generating random numbers without replacement***From:*Michael McCulloch <mm@pinestreetfoundation.org>

**Re: st: generating random numbers without replacement***From:*Nick Cox <njcoxstata@gmail.com>

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