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From |
Austin Nichols <austinnichols@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: collapse and weights |

Date |
Mon, 26 Nov 2012 19:23:50 +0100 |

OP contacted me off-list to say: On Mon, Nov 26, 2012 at 7:16 PM, Tomáš Houška <xbender@gmail.com> wrote: > Dear Mr. Nicholson, > > thank you for your help on Stata collapse. But your command is exactly > what i have tried and what fails to accomplish my goal. > > Lets say you have variables "quantity" and "price", each one has two > observations, (2,4) and (3,6) respectively. Now my aim is to get two > new variables, that would say "sum of quantity" and "average price > weighted by quantity". If you use the command > > --collapse (sum) sum_q=quantity (mean) wavg_price=price [fw=quantity] -- > > you get wavg_price = 5 (which is correct; (2*3+4*6)/(2+4)), but for > sum_q you get "20" => which is the weighted sum (2*2+4*4). the > "fweight" bracket applies to the sum as well as to the mean. That is > the problem which I am trying to solve. I would be greatfull for any > tips on this. > > Regards > Tomas Obviously, the OP did not read the two lines of code I posted, nor my last name, very carefully. More generally, do you think it is better to repost off-list emails to the list, or to completely ignore them? In the past, I have ignored them as akin to spam, and in clear violation of the Statalist FAQ guidelines, but I am unsure as to which is a good general rule. On Mon, Nov 26, 2012 at 6:36 PM, Austin Nichols <austinnichols@gmail.com> wrote: > Tomáš Houška <xbender@gmail.com>: > Your goal is a bit hard to understand from the description--are you > saying you want the sum of q and the q-weighted mean of price? > Like: > g one=1 > collapse (sum) sum=one (mean) price [fweight=q], by(prod_group) > > On Sun, Nov 25, 2012 at 9:44 AM, Tomáš Houška <xbender@gmail.com> wrote: >> Dear Statalist, >> >> I have data containing weekly information on prices and quantities of >> sales of several products. These products can be divided into few >> groups and I would like to create for each group 1) an weighted >> average weekly price for the group where weight is the amounts of sale >> of each product in the group and 2) sum of sales of the products that >> belong to particular group. I will end up with average price and total >> sales for the given product group. >> >> But if I use >> -- collapse (sum) q (mean) price [fweight=q], by(prod_group) -- >> the weights get applied both to the average and the sum, which is not >> correct. I havent been able to come up with a solution how to bracket >> the stata command. Could someone please give me some guidance? >> Thank you! >> Tomas (PhD student) * * 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/

**References**:**st: collapse and weights***From:*Tomáš Houška <xbender@gmail.com>

**Re: st: collapse and weights***From:*Austin Nichols <austinnichols@gmail.com>

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