I produce here two codes with a slight difference that produce the same output. These codes are based on rangerun.

Code:
code #1

capture program drop one_regression
program define one_regression
    regress rt mkt mkt2
    predict resid, resid
    summ resid, detail
    gen double skewness = r(skewness)
    gen obs  = r(N)
    gen double mean = r(mean)
end

bysort stock_id mdate (date): gen high = cond(_n==1., mdate, -11)
rangerun one_regression, by(stock_id) interval(mdate -11 0)

collapse(mean) mdate obs stock_id skewness, by (stock year month)
order stock year month mdate obs stock_id skewness
and the code #2

Code:
Code #2

capture program drop one_regression
program define one_regression
regress rt mkt mkt2
 predict resid, resid
 summ resid, detail
 gen double sd = r(sd)
 gen double skewness = r(skewness)
 gen obs  = r(N)
 gen double mean = r(mean)
end
rangerun one_regression, interval(mdate -11 0) by(stock_id)

collapse(mean) mdate obs stock_id skewness  , by (stock year month)
order stock year month mdate obs stock_id skewness
The difference is that the Code #2 doesn't have the following line:

Code:
bysort stock_id mdate (date): gen high = cond(_n==1., mdate, -11)
Can somebody explain what role does this line have in the code #1.