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From |
tiago.pereira@incor.usp.br |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Why do some observations fail to be stored when I use a loop with more than 200 observations |

Date |
Sun, 28 Oct 2007 14:24:04 -0300 (BRT) |

Dear all, I have found the a problem, which, not surprisingly, I have no idea why it happens. I am using Stata 9.2 SE (Windows XP emulated in Fedora). Concisely, I wish to run a loop, compute a statistic, and store the results in my current dataset. In this respect, the problem relies on the fact that some observations of the statistic of interest are not computed/stored. For example, suppose I want to compute a P value from an exact test. Letīs consider the exact p value obtained by -genwhi-, a program used in Genetics. ----- Example 1 --------------- clear local example 10 set obs `example' gene a = round(uniform()*25) gene b = round(uniform()*25) gene c = round(uniform()*25) qui gene p_example=. forvalues i = 1/`example' { qui genhwi `=a[`i']' `=b[`i']' `=c[`i']' qui replace p_example = r(p_exact) in `i' } ---- End Example 1 ----------- Using the example just described above, I successfully get all results without problems. Nevertheless, if I increase the number of observations, say, local example 1000, then several observations are not computed/stored. For example: a b c p_example 15 7 4 .5175038 7 11 3 . 23 20 18 . 8 10 22 . 0 20 20 .0000885 17 23 1 .0132223 10 12 15 1 . . . 6 2 20 16 16 12 .0000974 4 17 16 7 2 8 .4895405 Interestingly enough, this also happens when all observations are equal, that is: ----- Example 2 --------------- clear local example 1000 set obs `example' gene a = 25 gene b = 50 gene c = 25 qui gene p_example=. forvalues i = 1/`example' { qui genhwi `=a[`i']' `=b[`i']' `=c[`i']' qui replace p_example = r(p_exact) in `i' } ---- End Example 2 ----------- which gives: a b c p_example 25 50 25 . 25 50 25 1 25 50 25 . 25 50 25 1 25 50 25 1 25 50 25 1 25 50 25 . 25 50 25 1 . . . 25 50 25 . 25 50 25 1 25 50 25 . I do not have Stata 10 in my home PC, but will try to investigate if the same problem occurs in that version of Stata. If you have any tip and/or suggestions, I will be, as usual, appreciating your time and help. Regards, Tiago * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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