you can just add a conditional statement before running the reg, for example, suppose 100 is the min sample size you want for running the reg

forv I=1/100 {
count if group==`i'
if r(N)>=100 {
reg ..........................
}
}


if you have very small sample size, even if bigger than you DF requirement, does it make sense to run reg?

我想要的是，只要满足自由度条件的就回归，不满足的就不进行。

then just change 100 to what ever number you want.