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From |
Zeynep Ozkok <zeynepozkok@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: creating loops using combinations of variables |

Date |
Thu, 16 Feb 2012 12:59:42 +0100 |

Hi, Thank you very much for your comment Nick. Let me try to clarify the issue a bit by taking three variables as you suggested. On Thu, Feb 16, 2012 at 11:41 AM, Nick Cox <n.j.cox@durham.ac.uk> wrote: > "All possible combinations" would usually mean, for 27 variables, 27 ways of selecting just one, comb(27, 2) = 351 ways of selecting two, ..., up to comb(27, 27) = 1 way of selecting them all. In total that means 2^27 - 1 ~ 10^8 combinations. That is, precisely, 134,217,727 combinations. > > My suggestion is to set aside the fact that you have 27 variables. Show us exactly what you would do with just 3 variables, say. > > Nick > n.j.cox@durham.ac.uk > > Zeynep Ozkok > > I have a question on how to create loops for combinations of different > variables. I have 27 variables that I would like to put in two different > indices. > > The indices can be constructed in two steps: > > Lex1=sum(of different variables out of 27) this variable should be able > to take on 1 to 27 variables, so it should allow for all possible > combinations. It could be equal to only 1 variable, or it could be equal to > the sum of different variables > > Index1 = ln (1+lex1) this index is then dependent on what values lex1 > takes on > > Similarly > > Lex2 = sum (of all the variables that are not accounted in lex1) again this > could take on one variable, or more than one depending on the structure of > lex1. > > Index2 = ln(1+lex2) this index is once again dependent on what values lex2 > takes on, which is dependent on the values that lex1 takes on. > > Then these two indices will simultaneously be used in fixed effects > regressions as follows: > > Y_i,s,t= alpha_i +alpha_s +alpha_t +beta*(index1)_i,t +lamda* (index2)_i,t > + error_i,s,t > > The loop must go on until all possibilities/ combinations are completed. I > need to check the results of the beta and lamda coefficients and their > corresponding rsquares for each regression. Since there are numerous > possibilities in constructing each index I need to create a loop. However I > don't even know how to start out a loop that depends on combinations of > variables. Could you possibly help me out in writing and solving this > problem? > > > * > * 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/

**Follow-Ups**:**Re: st: RE: creating loops using combinations of variables***From:*Zeynep Ozkok <zeynepozkok@gmail.com>

**References**:**st: creating loops using combinations of variables***From:*Zeynep Ozkok <zeynepozkok@gmail.com>

**st: RE: creating loops using combinations of variables***From:*Nick Cox <n.j.cox@durham.ac.uk>

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