cond函数作用：
cond(x,a,b,c) or cond(x,a,b)
       Domain x:     -8e+307 to 8e+307 and missing; 0 means false, otherwise interpreted as true
       Domain a:     numbers and strings
       Domain b:     numbers if a is a number; strings if a is a string
       Domain c:     numbers if a is a number; strings if a is a string
       Range:        a, b, and c
       Description:  returns a if x is true and nonmissing, b if x is false, and c if x is missing.
                     returns a if c is not specified and x evaluates to missing.

                     Note that expressions such as x>2 will never evaluate to missing.

                         cond(x>2,50,70) returns 50 if x > 2 (includes x > .)
                         cond(x>2,50,70) returns 70 if x < 2


quietly是为了不输出结果在屏幕上。

嗯，回复您晚了，很感谢您的热心回复。学习了。

duplicates drop即可。这样子，如果两条记录在所有变量上的取值完全一样，就会有一条记录被删掉。

顶楼上，duplicates drop就可以了。感觉这种方法更简便。

duplicates drop不具有普遍性，不适用于有多个变量，只想去掉其中两个变量取值相同的观测值。

请问下，该怎么做呢？

您的这个命令帮了我大忙，谢谢您！

[quote]ywh19860616 发表于 2013-8-17 10:50 资料来源：
https://www.stata.com/support/faqs/data-management/duplicate-observations/
Case 1: Identifying duplicates based on a subset of variables
You wish to create a new variable named dup

         dup = 0       record is unique
         dup = 1       record is duplicate, first occurrence
         dup = 2       record is duplicate, second occurrence
         dup = 3       record is duplicate, third occurrence
         etc.
and to base the determination on the variables name, age, and sex.

        . sort name age sex
        . quietly by name age sex:  gen dup = cond(_N==1,0,_n)
Note the capitalization of _N and _n. (Stata interprets _N to mean the total number of observations in the by-group and _n to be the observation number within the by-group.)

Having created the new variable dup, you could then

        . tabulate dup
to see a report of the duplicate count.

To base the duplicate count solely on name, type

        . sort name
        . quietly by name:  gen dup = cond(_N==1,0,_n)

这个命令会报错。抄袭2008年的连享会的答案也多少动点脑子操作一下吧？