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From |
Ichiro Fujikake <fujikake@cc.miyazaki-u.ac.jp> |

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

Subject |
Re: st: Getting Panel Data Ready for Survival Analysis |

Date |
Thu, 24 Feb 2005 16:29:05 +0900 |

Hi Jason, How about drop if quantity==0 bysort sid pid bid (year): keep if _n==1 for (1), and, bysort sid pid year (quantity) : keep if _n==1 gen answer=year if quantity>=50 bysort sid pid (answer): keep if _n==1 for (2)? For (1) you can change the order of the two commands. But I suppose restricting sample first is faster (but insignificantly maybe). Ichiro On 05.2.24 13:46, "Jason Hwang" <jjhwang@fas.harvard.edu> wrote: > Dear Statalist Users, > > I have panel data and I would like to extract certain information for a > survival analysis. Conceptually, I have data on supplier, buyer and > quantity sold and I want to ask: when is the first date at which buyer > buys more than x amount. > > My data is of the following form: > > year sid pid bid quantity > 1990 111 1 555 0 > 1990 111 1 777 10 > 1990 111 2 555 100 > 1990 111 2 777 0 > 1991 111 1 555 3 > 1991 111 1 777 25 > 1991 111 2 555 5 > 1991 111 2 777 5 > > sid: seller id > pid: product id > bid: buyer id > > So this tells me for each seller, how much product they sold to which > buyer. Now I want to ask two questions: > > (1) For each seller and for each product and buyer, when is the first year > at which quantity sold is positive? > > So the output I would want would be: > > sid pid bid answer > 111 1 555 1991 > 111 1 777 1990 > 111 2 555 1990 > 111 2 777 1991 > > The complication is that in the real data, quantity sold may become > positive, zero, then again positive. How can I only pick up the first time > it becomes positive? > > With this simple data, it's relative easy. I can just sort by sid pid bid > and pick the first year that comes up but I was wondering if there's a > more elegant way that's also quicker. > > (2) This is trickier. For each selle and product, I want the first year at > which quantity sold is at least x for all buyers. For example, say x=50. > mThen my answer would be > > sid pid answer > 111 1 . > 111 2 . > > since in neither year does the seller sell more than 50 to ALL buyers. > > However if x=5, then the output woud be > > sid pid answer > 111 1 . > 111 2 1991 > > I would appreciate any hints. Any references or tricks for getting this > type of panel data ready for survival-type analysis would be helpful as > well. Thank you very much for your help. > > Jason Hwang > * > * 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/ > * * 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/

**References**:**st: Getting Panel Data Ready for Survival Analysis***From:*Jason Hwang <jjhwang@fas.harvard.edu>

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