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From |
Tomáš Houška <xbender@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: looping panel data |

Date |
Tue, 4 Oct 2011 13:50:25 +0200 |

Hi Nick, thank you very much for the answer and for pointing out the typo. I forgot about --by-- option with --egen-- command. One more thing I would like overcome is that when any observation of any of the variables in the expresion is considered missing, the result for that whole row is zero - intuitivelly it should skip summing up of missing values and just give the result of the rest of summing the expression. But even when only one multiplication contains missing values, the overall result for that row is zero. That is the result is zero even though there are pairs of prices and exp_shares that would produce a real number after multiplication. Is there some way to deal with that? I have tried replacing all the missing obs in all variables with zeros and then I get an actual number in the sum - but I feel it would be cleaner to define that in --egen-- commnad rather than to change all variables involved in the expression. Thank you! Tomas 2011/10/4 Nick Cox <n.j.cox@durham.ac.uk>: > You are a bit confused about -foreach- syntax, but that is secondary. (I think you meant to use `store' within the loop, not `store_number'.) > > However, I don't see a need for any loops here. This should be one line of Stata. The basic trick is > > egen P_nt = total(expression), by(store week) > > Your expression is > > exp_share9401000* avgp9401000+ > exp_share9401870* avgp9401000+ exp_share9402500* avgp9402500+ > exp_share9402600* avgp9402600+ exp_share9405400* avgp9405400+ > exp_share9408160* avgp9408160+ exp_share9410100* avgp9410100+ > exp_share9410200* avgp9410200+ exp_share9450850* avgp9450850+ > exp_share9451200* avgp9451200+ exp_share9451000* avgp9451000 > > except that it looks as if there is a typo there and it should be > > exp_share9401000* avgp9401000+ > exp_share9401870* avgp9401870+ exp_share9402500* avgp9402500+ > exp_share9402600* avgp9402600+ exp_share9405400* avgp9405400+ > exp_share9408160* avgp9408160+ exp_share9410100* avgp9410100+ > exp_share9410200* avgp9410200+ exp_share9450850* avgp9450850+ > exp_share9451200* avgp9451200+ exp_share9451000* avgp9451000 > > Nick > n.j.cox@durham.ac.uk > > Tomáš Houška > > I would like to ask you for a help with my looping problem. I have > sales panel data with variables week ID, store ID, product ID, price, > expenditure_share (share of expenditures for a given product across > all products in dataset) > > I would like to compute Stone price index defined as P_nt=SUM > (expenditure_share_int * P_int ). This means that for each combination > of store (n) and week (t) I need to compute a multiple of > expenditure_share and price for each product (i) and then sum it up > over all products sold in the particular store that week. The result > is again a panel data variable P_nt which is a price index for each > week and store. It is an expenditure system index, so the more you > spend on more expensive products (keeping prices constant), the higher > the index. > > And I cannot figure out a way how to calculate P_nt index. I have come > up with a loop, which saves the results in a new dataset, but it is > not working. I would be very glad for any help on how to calculate > this variable. > > Here is my looping command (j=week number, store_number is a local > macro with list of store numbers - they are from 2-131 but with > missing values (i.e. not consecutive)) > > postfile index_file store week index using stone_index_res, replace > foreach store in `store_number' { > forvalues j=91/317 { > gen index`store_number'`j' = exp_share9401000* avgp9401000+ > exp_share9401870* avgp9401000+ exp_share9402500* avgp9402500+ > exp_share9402600* avgp9402600+ exp_share9405400* avgp9405400+ > exp_share9408160* avgp9408160+ exp_share9410100* avgp9410100+ > exp_share9410200* avgp9410200+ exp_share9450850* avgp9450850+ > exp_share9451200* avgp9451200+ exp_share9451000* avgp9451000 if > week==`j' & store==`store_number' > post index_file (`week') (`store') (index`store_number'`j') > } > } > postclose index_file > > > * > * 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: RE: looping panel data***From:*Nick Cox <n.j.cox@durham.ac.uk>

**References**:**st: looping panel data***From:*Tomáš Houška <xbender@gmail.com>

**st: RE: looping panel data***From:*Nick Cox <n.j.cox@durham.ac.uk>

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