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

To |
"statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu> |

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

Date |
Sat, 25 May 2013 08:15:27 -0700 |

Thanks for the suggestions on learning Mata. On my sampling exercise, I articulated my request for guidance incorrectly. What I seek to do is, for each level of varA (n=5), generate an observation in which varB is a randomly chosen non-repeating value between 1-5. Best wishes, Michael McCulloch -- 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 25, 2013, at 12:40 AM, Nick Cox <njcoxstata@gmail.com> wrote: > The preceding specifications I take to mean > > "I wish to generate random numbers between 1 and 5, without replacement." > > I don't understand what this means as you don't say from what > distribution such numbers are drawn (discrete integers 1,2,3,4,5 or > continuous on the interval; uniform or stated alternative) or about > dependence or independence structure. I could speculate, but I would > rather you gave a precise specification. > > The only complete explanation of Mata is the manual. It's in flavour > an in-house manual for StataCorp's developers that happens to be > public to Stata users. (That's a bit tongue-in-cheek.) There's perhaps > a presumption that you are at least broadly familiar with programming > in a C-like language. Excessive familiarity with Stata is in some ways > a disadvantage as Stata is full of Stataish idiosyncrasies, starting > with heavy use of local and global macros. > > But cheer up... Quite a few people have written programs using Mata > without ever using more than a small fraction of the language. And > there is a very nice introduction in Kit Baum's book > > http://www.stata.com/bookstore/stata-programming-introduction/ > > Nick > njcoxstata@gmail.com > > > On 25 May 2013 06:23, Michael McCulloch <mm@pinestreetfoundation.org> wrote: >> 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/ > * > * 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>

**Re: 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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