webuse egenxmpl6,clear
browse
egen racesex = group(race sex)
// Create racesex containing values 1, 2, ...,
//for the groups formed by race and sex
//and containing missing if race or sex are missing
browse
2. 例子：汇率加权计算
clear
input firm country exch export
1 1 8 60
1 2 0.03 50
1 3 10 80
2 2 0.03 68
2 4 3 80
3 2 0.03 200
3 3 10 90
3 4 3 250
3 5 1.1 120
end
//【注】案例来源于连玉君老师STATA33讲
//加权计算汇率，权重是企业对每个国家出口额占该企业出口总额的比重
//计算公式为EER== (x1^w1)*(x2^w2)*(x3^w3)...*(xn^wn)
//xi表示各国汇率 wi表示出口比重
//由于STATA处理连乘困难，转化思路，对EER取对数
//ln(EER)== w1*ln(x1) + w2*ln(x2) + w3*ln(x3)
//第一步：对汇率取对数
gen lnexch = ln(exch)
//第二步：对每一个企业，分别计算他们的各国出口额占其出口总额的比重
bysort firm: egen weight = pc(export),prop
* pc(exp) [, prop] (allows by varlist:)
*returns exp (within varlist) scaled to be a percentage of the total,
*between 0 and 100.
*The prop option returns exp scaled to be a proportion of the total,
*between 0 and 1.
*第三步：计算weight和ln(exch)的乘积
gen wei_lnexch = weight*ln(exch)
*第四步：对每一个企业，将weight和lnexch的乘积加总起来
bysort firm: egen sum_wei = total(wei_lnexch)
gen EER = exp(sum_wei)