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From |
Joachim LandstrÃ¶m <joachim.landstrom@fek.uu.se> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
RE: st: RE: How to adjust the content of a local macro? |

Date |
Thu, 10 Dec 2009 14:01:38 +0100 |

/Joachim Quoting Nick Cox <n.j.cox@durham.ac.uk>:

The example is fine in terms of showing that you can use -local-sdirectly and do not need to call -tempname- for this purpose. (Themain use of -tempname- is for later use of scalars.) But note alsothat the -local-s are unnecessary:forv i =1/5{ capt drop myvar set obs 10 gen myvar=runiform() su myvar, mean di in r "min: `r(min)', max: `r(max)'" } Nick n.j.cox@durham.ac.uk -----Original Message-----From: owner-statalist@hsphsun2.harvard.edu[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of MartinWeissSent: 09 December 2009 22:49 To: statalist@hsphsun2.harvard.edu Subject: RE: st: RE: How to adjust the content of a local macro? <> " I will have the -meanonly- option in mind. Did not know about it. :)" Re -summ, meanonly-, you may also want to read NJC`s http://www.stata-journal.com/article.html?article=st0135 " I am indeed confused with the Stata usage of ` ' and have been having problems with this. minDate is a -tempname- so if I just write `minDate' I don't get the value, just the tempname. Doing it as ``minDate'' provides me with the value. But I am sure there are smarter ways to do this. . ." Why do you need -tempname-s here, anyway? See the example where I can reassign the minimum and maximum repeatedly w/o -tempname-s: *** forv i =1/5{ capt drop myvar set obs 10 gen myvar=runiform() su myvar, mean local min=r(min) local max=r(max) di in r "min: `min', max: `max'" } *** HTH Martin -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Joachim LandstrÃ¶m Sent: Mittwoch, 9. Dezember 2009 23:28 To: statalist@hsphsun2.harvard.edu Subject: Re: st: RE: How to adjust the content of a local macro? I am amazed with the level of help that you get from here. Let me start off expressing my gratitude for this. To answer some of Nick's points:1. The loop consists of repeated -drop-ping of observations not desired, working with the remaining subset and then a -restore- of the original. It is difficult to say in general what is most efficient and what most elegant but for a situation like that below I'd normally just add an extra condition excluding the observations not wanted, rather than repeatedly doing major surgery on the dataset. However, others could equally point out that applying -if- on a very large dataset can be time-consuming.Answer #1: I have been using -preserve- & -restore, preserve- in loops because of system limitations. I have a dataset as below Contains data from us_data_ret.dta obs: 17,516,468 vars: 5 10 Nov 2009 07:02 size: 525,494,040 (56.6% of memory free) ------------------------------------------------------------ storage display value variable name type format label variable label ------------------------------------------------------------- id int %8.0g ID dscd str6 %9s DSCD date float %td year int %8.0g totalReturn double %10.0g ----------------------------------------------------------- Sorted by: id date that I join with annual market data as below: Contains data from C:\Users\Joachim\AppData\Local\Temp\ST_02000005.tmp obs: 1,461 Total returns for value-weighted ave S/B & H/L BM portf and their diffs. See Fam vars: 5 9 Dec 2009 23:08 size: 46,752 (99.9% of memory free) ---------------------------------------------------------------------------- ---------------------------- storage display value variable name type format label variable label ---------------------------------------------------------------------------- ---------------------------- date float %td SMBtr float %9.0g Small-Minus-Big Total Returns. See Fama & French (1993). HMLtr float %9.0g High-Minus-Low Total Returns. See Fama & French (1993). riskFreereturn float %9.0g US T-Bill 3 month, middle rate marketReturn double %9.0g Frank Russel 3000, Total Return Index ---------------------------------------------------------------------------- --------------------------- Sorted by: The first dataset above is in "long format" and has 10826 unique ids (US firms). The date variable ranges from 03Jan1978 to 30dec2008 with weekly stock market data. Then I wish to do a Fama & French 3F CAPM calculation per id and then, based on the 3F CAPM I wish to calculate the expected annual return for each firm-year when each firm is traded on the stock market. Now I know I may be using too much lingo, but this boils down to an OLS regression per id provided that enough data is available (for me that implies three years of weekly data). Since I do not have enough computing power/memory (I am using a Windows 32-bit system) to add more variables into the joined dataset I have resorted use the -preserve- & -restore, preserve- method to drop all but a single id and then do the necessary operations on that subset. Then I save the data into a tempfile. Later (after 6-7 hours), when the loop is done I use -append- to build the dataset anew (having dropped unnecessary data). Any suggestions to more elegant methods are greatly appreciated.2. If only the minimum and maximum are needed from a -summarize- it is best just to use a -meanonly- option. (The name -meanonly- is misleading, as I've had occasion to remark before.)I will have the -meanonly- option in mind. Did not know about it. :)3. Code like local `minDate' = r(min) <stuff> if <stuff> date >= ``minDate'' looks legal but odd. You are probably using more levels of macros than you need. It's hard to tell because the code isn't completely self-contained (that's not a criticism; it wasn't necessary for your question).I am indeed confused with the Stata usage of ` ' and have been having problems with this. minDate is a -tempname- so if I just write `minDate' I don't get the value, just the tempname. Doing it as ``minDate'' provides me with the value. But I am sure there are smarter ways to do this. . .4. Code in which you loop over the contents of a local macro and change that macro within the loop can be tricky. Watch out!My computer at the university is running a test this evening with the revised code and I was intuitively also worried to change -panelVar- inside the loop which it guides. I have done it as Martin proposed and added a -adjustedPanelVar- that I modify. I need it for a second loop where I append the dataset once the first loop is done.5. The -if- condition in summarize totalReturn if totalReturn != . is unnecessary as -summarize- always ignores missings.That is always good to know.6. To get minimum and maximum dates in a panel, no looping is necessary as egen mindate = min(date), by(id) egen maxdate = max(date), by(id) will do it. Similarly it looks as if your main problem does not need any looping either, as it should yield to -egen- operations. Look at -egen, count()- in particular.Yes I have used -min()-elsewhere but I cannot easily add more variables to the complete database due to memory limitations. Memory is a luxury to me. . .7. More generally, it is not always positive to know too many other languages if they lead you to seek a Stata equivalent of other code when there's a Stataish way to do it without any real programming.I completely agree. Coming from SAS I am used to -proc sql- and SAS' -proc iml-. Had I just known about STATA 1998 this would not have been a problem. Now I have to "delearn" the SAS version of sql while learning STATA and that is like a baby learning to walk. I try my best but keep bruising myself. . . :) I will respond to Martin's second post tomorrow by posting the code and an an excerpt of the data (beware that it looks much like crochet since I have mainly been trying to get the code to run without exiting with errors). /Joachim * * 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/ * * 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/ * * 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/

-- Joachim Landström * * 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/

**References**:**st: How to adjust the content of a local macro?***From:*Joachim Landström <joachim.landstrom@fek.uu.se>

**st: RE: How to adjust the content of a local macro?***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**Re: st: RE: How to adjust the content of a local macro?***From:*Joachim LandstrÃ¶m <joachim.landstrom@fek.uu.se>

**RE: st: RE: How to adjust the content of a local macro?***From:*"Martin Weiss" <martin.weiss1@gmx.de>

**RE: st: RE: How to adjust the content of a local macro?***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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