Generating variable loop error

[Giorgio Di Stefano]

Dear all,

I am running a loop for panel data. Their aim is to obtain some kind of optimal value from a regression of var1 on var2. I am having about 80 countries in the sample and when I run the loop on the first country I get the error

"country_name" not found

I switched, but not desired, variable "country" with the panel identifier "ID" and got

 invalid 'and'

I've run the code by substituting my two variables with two others and got again the

 invalid 'and'

error
Thank you

Here is my code below. Can you please tell why and where I am wrong?

levelsof id, local(con)
levelsof year, local(time)

foreach i of local con{
foreach j of local time{
regress var1 c.ivar2##c.var2 if id == `i' and year ==`j'
generate optiVar3`i'`j' = -_b[var2]/(2*_b[var2 #ivar2 ])
generate optvar4`i'`j' = _b[var2 ]*var2 + ... ...
}
}

Giorgio!

[Andrew Musau]

Stata syntax is easy to write, but StataCorp hasn't gotten to incorporating the "and" yet!

regress var1 c.ivar2##c.var2 if id == `i' & year ==`j'

[Nick Cox]

help statsby would be an easier framework here.

[Giorgio Di Stefano]

Stata syntax is easy to write, but StataCorp hasn't gotten to incorporating the "and" yet!

regress var1 c.ivar2##c.var2 if id == `i' & year ==`j'

Thank you.@Andrew Musau and Nick Cox !. I had missed that. Now, after I corrected the program, I get two errors: Either

no observations

or

insufficient observations

. That's strange because I have a balanced panel.
Any ideas please?

[Andrew Musau]

In panel data, a specific id-year combination defines a single observation. You cannot run a regression with a single observation.

webuse grunfeld, clear
xtset company year
list if company==1 & year==1945
xtreg invest mvalue kstock if company==3 & year==1945

Res.:

. xtset company year
       panel variable:  company (strongly balanced)
        time variable:  year, 1935 to 1954
                delta:  1 year

. 
. list if company==1 & year==1945

     +--------------------------------------------------+
     | company   year   invest   mvalue   kstock   time |
     |--------------------------------------------------|
 11. |       1   1945    561.2   4840.9      265     11 |
     +--------------------------------------------------+

. 
. xtreg invest mvalue kstock if company==3 & year==1945
insufficient observations
r(2001);