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

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

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

Date |
Tue, 4 Oct 2011 15:44:27 +0100 |

What I think you want is local exp local avgp foreach j of local item_code { local exp `exp' exp`j' local avgp `avgp' avgp`j' } What's going on here is explained in [U]. Nick n.j.cox@durham.ac.uk Tomáš Houška Thank you for the info.... I am trying to run a loop comparable to the one you have written, but it is not producing the expected output. I have product identifiers: 9401000 9401870 9402500 9402600 9405400 9408160 9410100 9410200 9450850 9451200 9451000 and I would like to use them to group variables together into macros. I have adjusted the loop you have sent to: local item_code 9401000 9401870 9402500 9402600 9405400 9408160 9410100 9410200 9450850 9451200 9451000 foreach j of local item_code { local exp = exp`j' local avgp = avgp`j' } the loop is working in the sence that if I insert a --display-- command there, the values of item_code are displayed. But the local macro is not created... even if I replace the "local item_code" in the first line with the actual list of codes "foreach j in ...". What am I not getting? Since I am working with many variables and many products, this would be a real time saver. Thanks, Tomas PS: I am getting confused with underscores in the macro names. If I use command --local item_code .....--, for listing the items I have refer to it with underscore "_item_code" - should that be in the --foreach-- command too? (i.e. "foreach j of _item_code") 2011/10/4 Nick Cox <n.j.cox@durham.ac.uk>: > That said, if your interpretation is really that "missing" should be treated as "zero", then you will have repeated problems working with these data unless you -mvencode-. > > Nick > n.j.cox@durham.ac.uk > > > -----Original Message----- > From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox > Sent: 04 October 2011 13:10 > To: 'statalist@hsphsun2.harvard.edu' > Subject: RE: st: RE: looping panel data > > I don't know a way to do this all in -egen-. As far as -egen- is concerned the argument supplied is a single expression. > > But it sounds like > > gen total = 0 > gen work = . > > foreach j in 9401000 9401870 9402500 9402600 9405400 9408160 9410100 9410200 9450850 9451200 9451000 { > replace work = exp_share`j' * avgp`j' > replace total = total + work if !missing(work) > } > > egen P_nt = total(total), by(store week) > > Using an intermediate variable -work- is not essential. > > Nick > n.j.cox@durham.ac.uk > > > -----Original Message----- > From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Tomáš Houška > Sent: 04 October 2011 12:50 > To: statalist@hsphsun2.harvard.edu > Subject: Re: st: RE: looping panel data > > 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/

**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>

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

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

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

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

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