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From |
"Newson, Roger B" <r.newson@imperial.ac.uk> |

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

Subject |
RE: st: Does Blasnik's Law apply to -use-? |

Date |
Sun, 16 Sep 2007 15:19:09 +0100 |

Thanks to David Elliot, Mike Blasnik and David Airey for their very helpful and detailed replies to my query. These shall be used to inform the first Stata 10 update to -parmby-, when I have Stata 10. And thanks also to Vince Wiggins, who warned me (during the 13th UK Stata User Meeting last week) of the dangers of ordinary users trying to get too deep into the undocumented _prefix suite of commands, used internally by StataCorp for -statsby- and other prefixes. (In Stata, type whelp _prefix to find out more about these.) Best wishes Roger Roger Newson Lecturer in Medical Statistics Respiratory Epidemiology and Public Health Group National Heart and Lung Institute Imperial College London Royal Brompton campus Room 33, Emmanuel Kaye Building 1B Manresa Road London SW3 6LR UNITED KINGDOM Tel: +44 (0)20 7352 8121 ext 3381 Fax: +44 (0)20 7351 8322 Email: r.newson@imperial.ac.uk Web page: www.imperial.ac.uk/nhli/r.newson/ Departmental Web page: http://www1.imperial.ac.uk/medicine/about/divisions/nhli/respiration/pop genetics/reph/ Opinions expressed are those of the author, not of the institution. -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of David Elliott Sent: 14 September 2007 15:07 To: statalist@hsphsun2.harvard.edu Subject: Re: st: Does Blasnik's Law apply to -use-? Being Stata users, we should approach this in a rigorous scientific fashion: X-----begin-----X program define intest version 9.0 *! version 1.0.0 2007.09.13 *! Simulate using part of file with in #/## *! by David C. Elliott *! *! using name of trial dataset *! postname specifies filename of postfile *! numblocks is number of file blocks to create syntax using/ ,POSTname(string) NUMblocks(int) local more `c(more)' set more off use `using', clear //Load first to eliminate any first pass caching effects local recblock = round(`c(N)'/`numblocks',1) tempname post postfile `post' double block float timein timeif using `postname', every(10) replace timer clear 1 n di _n(2) "{txt}{col 11}{center 10:-- IF --}{center 10:-- IN --}" _n /// "{center 10:Block}{center 10:Time}{center 10:Time}" _n /// "{hline 30}" local lastblock = `c(N)' - `recblock' forvalues i=1(`recblock')`lastblock ' { local block = `i' foreach I in if in { if "`I'" == "in" { local ifin in `i'/`=`i'+`recblock'' } else { local ifin if inrange(_n, `i', `=`i'+`recblock'') } timer on 1 use `using' `ifin', clear timer off 1 qui timer list 1 local time`I' :display %5.2f round(`r(t1)',.01) timer clear 1 } post `post' (`block') (`timein') (`timeif') n di "{res}{ralign 10:`block'}{ralign 10:`timeif'}{ralign 10:`timein'}" } postclose `post' set more `more' use `postname', clear lab var block "Record Block" lab var timein "Load Time using IN" lab var timeif "Load Time using IF" tw line timein block || line timeif block end X-----end-----X eg: . intest using dss_data_06_07.dta , postname(intest.dta) numblocks(100) -- IN -- -- IF -- Block Time Time ------------------------------ 1 0.64 0.88 17278 0.47 0.77 34555 0.47 0.77 51832 0.47 0.78 69109 0.45 0.78 86386 0.45 0.78 103663 0.47 0.78 120940 0.47 0.77 ... This adofile will run an -if- versus -in- simulation and graph the results. From my findings I can confirm a speed advantage of about 50% using -in- on dataset with obs:1,727,673 vars:28 size:266,061,642 However, things get murkier. Run a simulation, then max out Stata's memory setting with as much memory as the system will give you and run the simulation again. When you do this, you eliminate the system's ability to cache the file. Ordinarily, subject to filesize and available memory, Stata may be reading the file from cache. If this is the case, one will see an advantage to using -in-. However, if the caching advantage is eliminated by increasing Stata memory, my simulations show the speed reduction using -in- is negated. I also tested this on large network databases and was unable to demonstrate any advantage to -in-. So back to Roger's initial question. It would appear that for cacheable filesizes and large numbers of bygroups a strategy using -in- might be feasible. There is an overhead penalty of setting up the bygroups to make them selectable using -in- involving sorts and the like. For a small number of bygroups the speed advantages might be lost, but for many levels and a large number of iterations there would be an advantage. DC Elliott * * 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/ * * 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/

**Follow-Ups**:**Re: st: Does Blasnik's Law apply to -use-?***From:*"Sergiy Radyakin" <serjradyakin@gmail.com>

**References**:**st: Does Blasnik's Law apply to -use-?***From:*"Newson, Roger B" <r.newson@imperial.ac.uk>

**Re: st: Does Blasnik's Law apply to -use-?***From:*"David Elliott" <dcelliott@gmail.com>

**Re: st: Does Blasnik's Law apply to -use-?***From:*"David Elliott" <dcelliott@gmail.com>

**Re: st: Does Blasnik's Law apply to -use-?***From:*"Michael Blasnik" <michael.blasnik@verizon.net>

**RE: st: Does Blasnik's Law apply to -use-?***From:*"Newson, Roger B" <r.newson@imperial.ac.uk>

**Re: st: Does Blasnik's Law apply to -use-?***From:*"Michael Blasnik" <michael.blasnik@verizon.net>

**Re: st: Does Blasnik's Law apply to -use-?***From:*"David Elliott" <dcelliott@gmail.com>

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