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From |
agostino@unical.it |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: reshaping data? |

Date |
Fri, 26 Oct 2012 13:31:39 +0200 |

dear Nick,

hope this clarifies best M. Quoting Nick Cox <njcoxstata@gmail.com>:

In that case I really don't understand what you are seeking. See also Yuval's comments. I've never come across a model in which there are a different number of predictors for different observations, although I am always happy to be educated. It seems to me that 1. Either you are applying a standard model, in which case you can give literature references. 2. Or this is a new model, in which case you need to explain how it would be set-up and estimated. Note that it's easy to get variables such as the mean of the other prices in the same family. SeeFAQ . . Creating variables recording prop. of the other membersof a group. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .N. J. Cox4/05 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 On Thu, Oct 25, 2012 at 3:39 PM, <agostino@unical.it> wrote:dear Nick, thanks for your prompt reply. Unfortunately, the number of items is not fixed best regards Maria Quoting Nick Cox <njcoxstata@gmail.com>:This model formulation makes me feel a bit queasy, but I think what you want is something like this. Suppose for concreteness the number of items is fixed at 8. (I don't see how this will work if the number is not fixed.) So, "for any value of 8" sort code_family code_item forval i = 1/8 { by code_family : gen P`i' = P[`i'] } Note that, contrary to your title, there is no -reshape- here as you want your observations to remain observations; at least that's my understanding. Nick On Thu, Oct 25, 2012 at 3:08 PM, <agostino@unical.it> wrote:I have to estimate the equation Q1=a+b1P1+b2P2+...bnPn+e Where Q1 is the quantity of item 1 sold by a supermarket during a week , P1 is the price of item 1 in that week, the other prices are those of the n items belonging to the same family of items. My data set is organized as follows: Code_item week Q P Code_family 789 1 8 2 1 790 1 25 4 1 791 1 9 1.3 1 792 1 12 2 1 800 1 7 2 2 801 1 20 1.2 2 802 1 11 1.6 2 803 1 12 2 2 And so forth for the other weeks and families... For each item, how can I include in my regression the prices of the other (n-1) items of the same family, ignoring the prices of the items belonging to other families?* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

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**Follow-Ups**:**Re: st: reshaping data?***From:*Nick Cox <njcoxstata@gmail.com>

**References**:**st: reshaping data?***From:*agostino@unical.it

**Re: st: reshaping data?***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: reshaping data?***From:*agostino@unical.it

**Re: st: reshaping data?***From:*Nick Cox <njcoxstata@gmail.com>

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