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

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

Subject |
st: RE: Re: Two "forvalues" loops working together |

Date |
Fri, 14 May 2004 11:18:55 +0100 |

This won't work yet, as constructs like `Y+10' won't work the way you want them to work. There is, as far as I know, no undocumented syntax for looping through two sets of values simultaneously. You can go `=`Y'+10' to get an evaluation on the fly. You can also go `X--' to get decrementing on the fly. But in this case, the problem is not a full-blown multiple loop problem: it can be reduced to a single loop, as Jean showed. There is, however, a trade-off between concision and clarity. In this case I would be driven mostly by the consideration that I might well want to come back to this code and understand it immediately and be able to modify it quickly. Clarity would like win over concision in favour of something like local X = 43 forvalues Y = 120(10)530 { local Y2 = `Y' + 10 predict prob`Y', pr0(`Y', `Y2') predict exp`Y', e0(`Y', `Y2') local where = `samp' - `X' local X = `X' - 1 replace prob = prob`Y' in `where' replace exp = exp`Y' in `where' } You can squeeze this to fewer lines with local X = 43 forvalues Y = 120(10)530 { predict prob`Y', pr0(`Y', `=`Y' + 10') predict exp`Y', e0(`Y', `=`Y' + 10') local where = `samp' - `X--' replace prob = prob`Y' in `where' replace exp = exp`Y' in `where' } and even fewer local X = 43 forvalues Y = 120(10)530 { predict prob`Y', pr0(`Y', `=`Y' + 10') predict exp`Y', e0(`Y', `=`Y' + 10') replace prob = prob`Y' in `=`samp' - `X'' replace exp = exp`Y' in `=`samp' - `X--'' } but I think many Stata users would find this more difficult to read. There is a much more detailed discussion of such parallel loops problems in Stata Journal 3(2):185-202 (2003). Nick n.j.cox@durham.ac.uk jean ries > Here is a suggestion. Hope it helps. > > local X 43 > > forvalues Y = 120(10)530 { > predict prob`Y', pr0(`Y',`Y+10') > predict exp`Y', e0(`Y',`Y+10') > replace prob=prob`Y' in `samp-`X'' > replace exp=exp`Y' in `samp-`X'' > loc X = `X' - 1 > } Amani Siyam > I wish to make two "forvalues" loops work together rather > than nested as > shown by my suggested code below. Is there a way I can do > that in STATA > > > local samp=_N+43 > set obs `samp' > foreach M of newlist prob exp { > gen `M'=. > } > intreg ptiming timing if ~npointer1, noskip intreg > forvalues Y = 120(10)530 ; X = 43(-1)1 { > predict prob`Y', pr0(`Y',`Y+10') > predict exp`Y', e0(`Y',`Y+10') > replace prob=prob`Y' in `samp-`X'' > replace exp=exp`Y' in `samp-`X'' > } > local samp=_N-43 > slist prob exp in `samp'/l > * * 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/

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