# Re: st: RE: question about calculating discounted sum

 From Robin Luo To statalist@hsphsun2.harvard.edu Subject Re: st: RE: question about calculating discounted sum Date Sun, 20 Feb 2005 22:36:34 -0800

```Ichiro,

It works perfect. Thank you so much!

Robin

On Mon, 21 Feb 2005 09:33:22 +0900, Ichiro Fujikake
<fujikake@cc.miyazaki-u.ac.jp> wrote:
> I am sorry. There was a typo. I meant
>
> sort firmid year
> by firmid: gen i=_n
> qui sum i
> local imax=r(max)
> gen sum=income
> forv j=1/`imax' {
>    local h= `j'-1
>    forv k=1/`h' {
>        by firmid: replace sum=sum+income[_n-`k']/(`k'+1) if i==`j'
>    }
> }
>
> Ichiro
>
> On 05.2.21 9:28, "Ichiro Fujikake" <fujikake@cc.miyazaki-u.ac.jp> wrote:
>
> > Hi Robin
> >
> > I hope the following codes help you.
> >
> > sort firmid year
> > by firmid: gen i=_n
> > qui sum i
> > local imax=r(max)
> > gen sum=income
> > forv j=1/`imax' {
> >     local h= `j'-1
> >     forv k=1/`j-1' {
> >         by firmid: replace sum=sum+income[_n-`k']/(`k'+1) if i==`j'
> >     }
> > }
> >
> > Ichiro
> >
> >
> > On 05.2.21 8:36, "Robin Luo" <rluosf@gmail.com> wrote:
> >
> >> Btw, Scott, concerning `=seq', do you have any idea about how to
> >> integrate a variable into "forvalue" loop?
> >>
> >> Many thanks!
> >>
> >> Robin
> >>
> >>
> >> On Sun, 20 Feb 2005 16:37:04 -0600, Scott Merryman <smerryman@kc.rr.com>
> >> wrote:
> >>> How about attacking this problem directly:
> >>>
> >>> bysort firm (year): gen num = _n
> >>> gen sum = 0
> >>> by firm: replace sum = income + income[1]/num[2] if num== 2
> >>> by firm: replace sum = income + income[1]/num[3] + income[2]/num[2] ///
> >>>         if num ==  3
> >>> by firm: replace sum = income + income[1]/num[4] + income[2]/num[3] + ///
> >>>         income[3]/num[2] if num ==  4
> >>> by firm: replace sum = income + income[1]/num[5] + income[2]/num[4] + ///
> >>>         income[3]/num[3] + income[4]/num[2] if num == 5
> >>> by firm: replace sum = income + income[1]/num[6] + income[2]/num[5] + ///
> >>> income[3]/num[4] + income[4]/num[3] + income[5]/num[2] if num == 6
> >>>
> >>> Hope this helps,
> >>>
> >>> Scott
> >>>
> >>> P.S.  `=seq' is the same as seq[1] or 1
> >>>
> >>>> -----Original Message-----
> >>>> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-
> >>>> statalist@hsphsun2.harvard.edu] On Behalf Of Robin Luo
> >>>> Sent: Saturday, February 19, 2005 1:18 PM
> >>>> To: statalist@hsphsun2.harvard.edu
> >>>> Subject: st: question about calculating discounted sum
> >>>>
> >>>> I need to calculate discounted sum for a variable in a panel data. My
> >>>> data is like:
> >>>>
> >>>>  FirmID      year     income
> >>>>    100        1980     50000
> >>>>    100        1981     51000
> >>>>    100        1982     54000
> >>>>    100        1983     60000
> >>>>    100        1984     59000
> >>>>    100        1985     62000
> >>>>    101        1970     18000
> >>>>    101        1971     18500
> >>>>    101        1972     20000
> >>>>    101        1973     24000
> >>>>
> >>>> Basically, the data is a panel data, grouped by "FirmID", with
> >>>> hundreds of frims. What I need to do is to calculate a moving
> >>>> discounted sum of income for each firm-year. That is, calculate a sum
> >>>> of income from a firm's first year to the current year, but each
> >>>> year's income will be discounted by that year's distance to the
> >>>> current year and the discount rate is the inverse of the distance
> >>>> "1/(current year - year +1)". For example, for firm 100 at 1982, this
> >>>> calculation would be like: 54000 + 51000*1/2 +50000*1/3, while for
> >>>> firm 100 at 1984 it would be like 59000 + 60000*1/2 + 54000*1/3 +
> >>>> 51000*1/4 + 50000*1/5. I tried the following program:
> >>>>
> >>>> by FirmID: gen seq=_n
> >>>>
> >>>> gen suminc=0
> >>>>
> >>>> quietly forval i=1/`=seq' {
> >>>>            by FirmID: replace suminc = suminc + income[`i']/(`=seq' - `i'
> >>>> +1)
> >>>>            }
> >>>>
> >>>> But problems are: 1) the loop seems not allowing "by" command; 2) the
> >>>> loop does not really launch, because even after I get rid of "by
> >>>> FirmID" the loop seems to go only one cycle instead of "_n" cycles.
> >>>>
> >>>> Many many thanks for any help!
> >>>>
> >>>> Robin Luo
> >>>
> >>> *
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> >
> >
> > *
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> >
>
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```