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

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

Subject |
st: RE: Panel Data Manipulation |

Date |
Fri, 4 Nov 2005 17:46:53 -0000 |

1. gen byte sold = volume > 0 & volume < . bysort sold seller buyer (year) : gen firstyear = year[1] if sold bysort seller buyer (firstyear) : replace firstyear = firstyear[1] 2. I did one; now you do one. Nick n.j.cox@durham.ac.uk Jason Hwang > I would appreciate help with the following panel data manipulation > problem. I have data of the form: > > seller year product buyer volume > ... > 100 1990 1111 200 100 > 100 1991 1111 200 200 > 100 1992 1111 200 250 > 100 1990 2222 200 . > 100 1991 2222 200 80 > 100 1992 2222 200 83 > 100 1990 2222 500 100 > 100 1991 2222 500 125 > 100 1992 2222 500 200 > ... > > The dot in volume means sales volume in that year was zero. I > would like > summarize the data by answering two questions. First, each > seller sells > many products to many buyers. Let "firstyear" be the first > year a given > seller sells anything to a given buyer. In the example above, for the > seller-buyer pair 100-200, "firstyear" would be 1990. Then > for every other > product 100 sells to 200 in subsequent year, I want to > calculate the gap > between year of first sale and "firstyear". I would like to generate a > table of the form: > > seller product buyer timegap firstyear > ... > 100 1111 200 0 1990 > 100 2222 200 1 1991 > 100 2222 300 0 1990 > ... > > Second, I would like to ask: for each seller, how much of the > increase in > total sales of each product is driven by changes in sales to existing > buyers or sales to new buyers. I would like to generate a table of the > form: > > seller product year change same new > ... > 100 1111 1991 100 100 0 > 100 2222 1991 105 25 80 > ... > > Note that from 1990 to 1991, the total sales of 2222 > increased by 105, of > which 25 came from increasing sales to an existing customer > 500, and the > rest 80 came from selling to a new customer 200. > > One complication is that sometimes a seller will make sales > with a given > buyer in one year, make zero sales the next year, and > generate positive > sales another year. In the case of this last year, I would > like to count > the sales as coming from "same" customer. > > I would very much appreciate your help. Thanks very much. * * 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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