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From |
Stephen Cranney <cranney.stephen@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Re-assigning local macro values within loops after each iteration |

Date |
Mon, 20 Aug 2012 13:15:22 -0600 |

Is there any way that I can retain the forvalues i = 1/`N' { syntax while using the while loop to make it continue generating after first generation? The `i' reference here is how I connect the child to not only the parent, so I would like to keep it if I could, but the parent's date-of-giving-birth to calculate the child's date-of-birth, etc. I have a hard time seeing how I can make these connections while relying on the while loop. Here's an example of the syntax I mean: replace generationnumber=generationnumber[`i']+1 if newvar`i'==1 replace parentid= id[`i'] if newvar`i'==1 replace birthdate= date[`i'] if newvar`i'==1 replace birthmonth= month[`i'] if newvar`i'==1 replace birthyear= year[`i'] if newvar`i'==1 In response to the second concern, since each data point is a unique month/year/id combination, doubling it basically replicates the individual parent's characteristics (which I then change with reference to the `i' value that I want to retain). The Xnewvar variable I create deals with the problem of replicating the replications, so in the end I have, for example, 1000 observations for person 1, and 1000 observations for each of her children. Thanks again, Stephen On Mon, Aug 20, 2012 at 12:36 PM, Nick Cox <njcoxstata@gmail.com> wrote: > The Catch-22 here is that telling us part of your problem and showing > us part of your code is not enough for anyone to get a complete > understanding of your problem, while telling us all of your problem > and showing us all of your code would not really help, as you would be > unlikely to get anyone to invest time in understanding it all. > > That said, there is an important misunderstanding here. The effect of > > local N = _N > forvalues i = 1/`N' { > > is to set up a loop with a particular upper limit that is fixed when > the -forvalues- loop starts. Changing the number of observations after > the loop has begun makes no difference to that, unless you change the > number in such a way that the loop terminates for other reasons. In > effect, you are "compiling" the number of observations into your code > when the loop starts, so that's fixed code. > > My suggestion is that you may find it easier to set this up as a -while- loop. > > local notdone = 1 > local N = _N > > while `notdone' { > > > > } > > with code within the loop to change > > local notdone = 0 > > as appropriate. That certainly permits the number of observations to change. > > That said, I am curious about the line > > expand 2, gen(newvar`i') > > which doubles the number of observations, just because of one > childbirth. Sounds like something out of the Alien* films to me, but > nothing like human demography? Shouldn't that -expand- be limited to > expansion of certain observations? > > Nick > > On Mon, Aug 20, 2012 at 7:02 PM, Stephen Cranney > <cranney.stephen@gmail.com> wrote: > >> I'm running a loop that loops over observations and generates new >> observations with expand when one of the observations has a certain >> value for one of the variables. (It's a population simulation that is >> simulating a new person when each childbirth=1, each observation is a >> month/year combination for a specific id). I initially set the macro >> at N= _N, but I want to re-set the macro every time it loops, this way >> the simulation can run past the second generation. As it is, it saves >> the initial _N value and terminates when that value is reached, but I >> would like to re-assign the macro so that it equals the value of _N >> after each expansion, allowing it to run into multiple generations >> until it terminates because of other parameters I've imposed. >> >> I have tried to place the macro within the loop to see if it will >> re-do it, but it does not seem to be working. My syntax so far: >> >> local N = _N >> forvalues i = 1/`N' { >> local N = _N >> if childbirth[`i'] == 1 { >> expand 2, gen(newvar`i') >> egen Xnewvar= rowtotal (newvar*) >> drop if Xnewvar>1 >> drop if Xnewvar== 0 & generationnum!= 1 >> drop Xnewvar >> replace generationnum=generationnum[`i']+1 if newvar`i'==1 >> ** A lot of code that differentiates the new child's demographic >> characteristics from the parent's >> } >> } >> > * > * 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-assigning local macro values within loops after each iteration***From:*Nick Cox <njcoxstata@gmail.com>

**RE: st: Re-assigning local macro values within loops after each iteration***From:*"Cohen, Elan" <cohened@upmc.edu>

**References**:**st: Re-assigning local macro values within loops after each iteration***From:*Stephen Cranney <cranney.stephen@gmail.com>

**Re: st: Re-assigning local macro values within loops after each iteration***From:*Nick Cox <njcoxstata@gmail.com>

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