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From |
Abhimanyu Arora <abhimanyu.arora1987@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: spell variable according to a criteria |

Date |
Wed, 4 Apr 2012 20:56:53 +0200 |

Thanks very much indeed, Nick, was waiting for your ingenious take on the problem. Cheers Abhimanyu PS-Yes, I was wrangling with sorting for a couple of hours. I still cannot comprehend fully but (different combinations of) sorting does seem to influence the results. In fact I simplified the post as there being just panel var and time, but actually the data is in the mutilevel-form—country, city and time On Wed, Apr 4, 2012 at 8:19 PM, Nick Cox <njcoxstata@gmail.com> wrote: > I can't see a difference here in terms of what Stata will do between > your first and second postings. > > In terms of your original problem, I see no need to -sort- each time > around the loop as no command changes the sort order. In fact I see no > need for a loop here at all. > > The problem appears to be this: > > Within panels, if -event- is 1 and -stretch- is # then -event- == 1 is > the start of a spell with at most an extra # observations afterwards. > > Let's think about an -event- and suppose that -stretch- is 7. Then can > we think of that of starting a count-down: 7, 6, 5, 4, 3, 2, 1, 0. > When we get to 0, the spell is finished. (NASA used to say > "Blast-off".) But presumably a new -event- can reset the count-down. > > Here is sample code setting up a fake dataset. > > set obs 100 > gen panel_id = cond(_n < 51, 1, 2) > bysort panel_id : gen time = _n > gen event = 1 if runiform() < 0.2 > gen stretch = ceil(18 * runiform()) if event == 1 > > Now the algorithm is just this: > > bysort panel_id (time) : gen inspell = stretch if _n == 1 > by panel_id : replace inspell = max(stretch, inspell[_n-1]-1) if _n > 1 > > Now your spells are defined by -inspell- being >= 0 and not missing. > > Nick > > On Wed, Apr 4, 2012 at 5:06 PM, Abhimanyu Arora > <abhimanyu.arora1987@gmail.com> wrote: > >> I think I managed. >> >> So in the line >> bys panel_identifier:replace event=1 if stretch[_n-(`i'+1)]>`i' & >> stretch[_n-(`i'+1)]!=. & event==. >> >> I changed to >> >> bys panel_identifier:replace event=1 if stretch[_n-`=`i'+1']>`i' & >> stretch[_n-`=`i'+1']!=. & event==. >> >> in order to evaluate the local macro at every loop. > > On Wed, Apr 4, 2012 at 5:40 PM, Abhimanyu Arora > >>> I have a (monthly) time indicator and a variable 'stretch' that >>> identifies the spell of an event. I need to create a dummy in case the >>> event took place or not. >>> Currently event=1 for the start of the event (an missing for the >>> rest). If stretch==1, event should equal 1 for the next time period. >>> If stretch =2 event=1 for 2 more time periods (besides the starting >>> time). >>> >>> I know that stretch ranges from 1 to 18 (but may not have the values >>> in between). >>> >>> When I try without using the following loop (putting in the numbers >>> manually that is), it seems OK, But with the following loop things >>> aren't quite right. >>> >>> local i=0 >>> while `i'< 18 { >>> bys panel_identifier:replace event=1 if stretch[_n-(`i'+1)]>`i' & >>> stretch[_n-(`i'+1)]!=. & event==. >>> sort panel_id time >>> local ++i >>> } >>> >>> Where does the mistake lie? > > * > * 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: spell variable according to a criteria***From:*Nick Cox <njcoxstata@gmail.com>

**References**:**st: spell variable according to a criteria***From:*Abhimanyu Arora <abhimanyu.arora1987@gmail.com>

**Re: st: spell variable according to a criteria***From:*Abhimanyu Arora <abhimanyu.arora1987@gmail.com>

**Re: st: spell variable according to a criteria***From:*Nick Cox <njcoxstata@gmail.com>

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