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st: RE: RE: create many variables at once |

Date |
Tue, 23 Jul 2002 11:17:21 -0400 |

Elisabeth Simantov, PhD wrote > Perhaps someone can help me with this. I am not a > programmer, so please be explicit. > New question. > I have 19 variables that start with the prefix me_ and 19 > variables that > start with the prefix ppg_ . They all have other letters after the > underscore, actually the same for each group of 19. > > I have to create the following 19 new variables: > newvars=(me_ * var1)+(ppg_ * var1) for each observation in the data set (510) > Is there a way for me to do this in one step. If not, can > you please tell me how? and Ronan Conroy replied > 1. Verify that the variables are in the same order. If > not, issue the -aorder- command to get them correctly > ordered. > > 2. Use the -for- command to define two lists of variables. > By default, the lists are called X and Y (in capitals). > There are ways of imposing your own naming conventions, > but you don't need that for a simple problem. > > . for var me_* \ var ppg_* : gen X_Y = (X * var1) + (Y * var1) > Nick Cox also suggested > Tacit in this is that there is a pairing between > the -me_*- and the -ppg_*- > > 1. Use -for- > ============ > > One way to do it is with -for-: > > for var me_* \ var ppg_* : gen stub_X_Y = var1 * (X + Y) > > Naturally you can devise your own naming convention. > > This presupposes that the two sets of variables > are both in an appropriate order in memory. > > order me_* ppg_* The above solutions reminded me that -for-'s functionality hasn't quite been subsumed by the introduction of -foreach- and -forvalues- as I have been prone to believe. In version 6, I was quite content using the set of looping commands (tokenize, while, etc.) and hadn't got to learning -for- just yet. Thus, when -foreach- and -forvalues- came about with Stata 7, I saw no reason to bother with it. But the solutions are excellent illustrations that -for-'s sometimes results in more succinct and, arguably, elegant solutions as it avoids unnecessary looping. To right the wrong, I looked up for.hlp once more and noted small inconsistency the examples provided. The last example reads: (begin excerpt) . for any male female: save c:\data\X if sex=="X" will not work. for will think there are three commands: save c: data X if sex=="X" Instead, you must type . for any male female: save "c:\data\X" if sex=="X" (end of excerpt) The last line won't work either since the syntax of save doesn't allow the [if exp] condition -- a non-feature that I, among others, wouldn't mind seeing implemented in -save- BTW. ;) (NB: I know it's been discussed on the list before) Patrick Joly [email protected] [email protected] * * 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**:**st: RE: RE: RE: create many variables at once***From:*"Nick Cox" <[email protected]>

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