gen variable= product(..) ?

[Nicolas Thomas Ewbank]

Hi Guys!

Is there an easier way of creating a product variable column than making a loop?
It seems kind of strange that it is possible to gen var= sum(...) but not gen var= product(...)

Hope you can help me out?
Kind regards

Nick Ewbank

ps: for clarification, I need the column output to look like this:
1 = 1,01
2= 1,01*1,02
3= 1,01*1,02*1,03
4= etc..

[Svend Juul]

clear
set obs 20
gen var=1.01
replace var = var[_n-1]*1.01 if _n>1
list

[Svend Juul]

clear
set obs 20
gen var=1.01
replace var = var[_n-1]*(1+ _n/100) if _n>1
list

[Nicolas Thomas Ewbank]

Thank you! This helps a lot. However I am calculating holding period returns for many companies. How can I implement this code for more than 1 variable?
This is the formula I'm using: product(t=1 to 756) (1+r_it)

Thank you in advance!

[Nick Cox]

I guess one reason for the lack of a product function is that their results vanish if one term is zero (producing puzzlement to some) and can cause overflow or underflow problems all too easily (ditto). The traffic in user support might make its inclusion a dubious extra for StataCorp. Still, I said that, not them.

In addition to Svend's tricks, which work for your examples, I note also exp(sum(log()) so long as all values are positive.