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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

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

Subject |
RE: st: Overriding a loop if 0 observations using tabstat |

Date |
Tue, 27 Apr 2010 18:07:56 +0100 |

Good question. I decided to do some timings to support -- or rebut -- my feeling that -count- which just counts should be faster than -summarize, meanonly- which does other stuff too and in turn than -summarize- which does other stuff too. But although that's the order the timings are closer than I guessed. Still, doing anything the quickest way does no harm and may give valuable speed-up for large problems. Here is one test script. Compare your experiences: clear set obs 100000 set seed 2803 gen y = runiform() set rmsg on qui forval i = 1/10000 { count if y > 0.5 } qui forval i = 1/10000 { su y if y > 0.5, meanonly } qui forval i = 1/10000 { su y if y > 0.5 } My timings were t=187.49; 254.49; 313.38, which no doubt shows up the Mesolithic age of my machine. Nick n.j.cox@durham.ac.uk Martin Weiss " As a small detail of efficiency, I would always recommend -count- rather than -summarize- for the purpose here." My earlier code did use -count-... What makes this thing more efficient, though? Both are built-in, so they probably enjoy a big advantage over everybody else anyway. So I guess the reason for your preference is the fact that -count- calculates fewer results than -su, mean-? Nick Cox A secondary theme here is that this kind of code gets very difficult to read, which makes it difficult to maintain and debug. I note that the condition intab1 == 1 & admit_ic == 1 & btwg < . is common to all the -summarize- and -tabstat- commands. That being so, you could get that out of the way like this preserve keep if intab1 == 1 & admit_ic == 1 & btwg < . <stuff> restore Your -tabstat- options that are constant can be put in a little bag: local opts stat(n mean median p25 p75 min max) col(stat) f(%9.0g) notot nosep Now <stuff> can be rewritten forv i = 0/5 { foreach y in male singlet { forv s = 0/1 { di "myga==`i' & `y'==`s'" qui su bwtg if myga==`i' & `y' if r(N) != 0 { tabstat bwtg if myga==`i', `opts' by(`y') } } } } Now it is easier to see what is going on. I added some cosmetic changes too, which this horrible mailer may well reverse. One puzzle: Did you mean to add the condition "& `y'" to the -summarize-? It means the same as & `y' != 0 -- which may or may not be what you want. As a small detail of efficiency, I would always recommend -count- rather than -summarize- for the purpose here. Nick n.j.cox@durham.ac.uk sara khan Many thanks Maarten for your advice. I managed to resolve it with the following code: forv i=0/5 { foreach y in male singlet{ forv s=0/1{ di "myga==`i' & `y'==`s'" qui su bwtg if myga==`i' & intab1==1 & admit_ic==1 & bwtg<. & `y' if r(N)!=0{ tabstat bwtg if myga==`i' & intab1==1 & admit_ic==1 & bwtg<., stat(n mean median p25 p75 min max ) by(`y') col(stat) f(%9.0g) notot nosep } } } } On Tue, Apr 27, 2010 at 12:56 PM, Maarten buis <maartenbuis@yahoo.co.uk> wrote: > > --- On Tue, 27/4/10, sara khan wrote: >> I just tried this but the output only shows the display >> results and nothing from tabstat. > <snip> > > -capture- works for me: > > *----------------- begin example --------------------- > sysuse auto, clear > forvalues i = 0/5 { > capture noisily tabstat mpg if rep78== `i', /// > s(n mean) by(foreign) > } > *-------------------- end example ------------------- > > In order to debug your loop I would build it step by step: > step 1: no looping, no locals, no -if- just a single -tatstat- command > step 2: add -capture noisily- > step 3: add some -if- conditions > step 4: build a single loop (e.g. over i but not over y) > etc. etc. * * 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: Overriding a loop if 0 observations using tabstat***From:*"Martin Weiss" <martin.weiss1@gmx.de>

**References**:**Re: st: Overriding a loop if 0 observations using tabstat***From:*sara khan <sarakhanum84@googlemail.com>

**Re: st: Overriding a loop if 0 observations using tabstat***From:*Maarten buis <maartenbuis@yahoo.co.uk>

**Re: st: Overriding a loop if 0 observations using tabstat***From:*sara khan <sarakhanum84@googlemail.com>

**RE: st: Overriding a loop if 0 observations using tabstat***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**AW: st: Overriding a loop if 0 observations using tabstat***From:*"Martin Weiss" <martin.weiss1@gmx.de>

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