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" <[email protected]> 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 <[email protected]>
> 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: [email protected] [mailto:owner-
>>> [email protected]] On Behalf Of Robin Luo
>>> Sent: Saturday, February 19, 2005 1:18 PM
>>> To: [email protected]
>>> 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
>>
>> *
>> * For searches and help try:
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>> * http://www.ats.ucla.edu/stat/stata/
>>
> *
> * For searches and help try:
> * http://www.stata.com/support/faqs/res/findit.html
> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/
>
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
