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

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

Subject |
st: RE: Collapsing Over Limited Set |

Date |
Thu, 15 Sep 2005 21:26:04 +0100 |

As I understand it, this is not a collapsing problem at all, as you want as many observations at the end as you start with. One way to approach this is to notice that sum of all others = sum of all - value for this which suggests the following line of attack: bysort product: gen ave_others = sum(markup) by product: replace ave_others = (ave_others[_N] - markup) / (_N - 1) This would need some tweaking if markup was ever missing: gen byte touse = markup < . bysort touse product: gen ave_others = sum(markup) if touse by touse product: replace ave_others = (ave_others[_N] - markup) / (_N - 1) Some searching would have pointed to a ragbag of tricks in How do I create variables summarizing for each individual properties of the other members of a group? http://www.stata.com/support/faqs/data/members.html Nick n.j.cox@durham.ac.uk Jason Hwang > I'm trying to generate a dataset of statistics by collapsing another > dataset, but each of the id's I'm collapsing by, I want to use every > observation in the dataset except the one for the id under > consideration. > Would there be a way to do this? > > For example, I have data of the form: > > company product markup > 100 31 .3 > 100 55 .2 > 111 31 0 > 111 55 .1 > 120 31 .1 > 120 55 .1 > > Now I want to ask the question: for each company, calculate > the average > markup of each product it produces, where the average is > taken over all > companies that sell the product except the company itself. So > I want to > end up with > > company product averagemarkup > 100 31 .05 > 100 55 .1 > 111 31 .2 > 111 55 .15 > 120 31 .15 > 120 55 .15 > > Obviously collapsing the data the standard way is not going > to do this. I > need to do this for hundreds of thousands of observations (hundreds of > companies and thousands of products) so am looking for a way > to do this that would be relatively quick. * * 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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