006 Stata循环：foreach

Stata中的循环有三类：

• while循环
• foreach循环
• forvalues循环
  其中，foreach和forvalues都可以看作是while循环的变种。两者的区别在于foreach跟的对象可以是宏、变量名和文件名等，而forvalues跟的必须是数字。

接下来我们介绍 foreach循环

   foreach lname {in|of listtype} list {
                commands referring to `lname'
        }

  Allowed are

        foreach lname in any_list {

        foreach lname of local    lmacname   {

        foreach lname of global   gmacname   {

        foreach lname of varlist  varlist    {

        foreach lname of newlist  newvarlist {

        foreach lname of numlist  numlist    {

    Braces must be specified with foreach, and

        1.  the open brace must appear on the same line as the foreach;

        2.  nothing may follow the open brace except, of course, comments; the first command to be executed must appear on a new line;

        3.  the close brace must appear on a line by itself.

*示例1
clear
set obs 100
gen x1 = rnormal()
gen x2 = rnormal()
gen x3 = rnormal()
gen x4 = rnormal()
gen x5 = rnormal()

foreach var in x1 x2 x3 x4 x5{
    disp ""
    disp ""
    disp "T-test: the mean of variable `var' is 0"
    ttest `var' = 0
}


*示例2
sysuse auto, clear

foreach v in mpg weight length{
    summarize `v'
}

在foreach循环中，如果选择所有变量，可以写成：

foreach var of varlist_all{
    command
}

或

foreach var of varlist * {
    command
}

参考资料
官方帮助文档
【爬虫俱乐部】精通Stata之数据整理