Stata 删除重复（非唯一）的成对值

我在Stata处理一个边缘列表，类型如下：

var1 var2
 a    1
 a    2
 a    3
 b    1
 b    2
 1    a
 2    b

我想删除非唯一对，例如1a和2b（对我来说，它们与a1和b2相同）。我该怎么办

。清楚的
. clear 

. input str1 (var1 var2) 

          var1       var2
  1.  a    1
  2.  a    2
  3.  a    3
  4.  b    1
  5.  b    2
  6.  1    a
  7.  2    b
  8. end 

. gen first = cond(var1 <= var2, var1, var2) 

. gen second = cond(var1 <= var2, var2, var1) 

. list 

     +------------------------------+
     | var1   var2   first   second |
     |------------------------------|
  1. |    a      1       1        a |
  2. |    a      2       2        a |
  3. |    a      3       3        a |
  4. |    b      1       1        b |
  5. |    b      2       2        b |
     |------------------------------|
  6. |    1      a       1        a |
  7. |    2      b       2        b |
     +------------------------------+

. duplicates list first second 

Duplicates in terms of first second

  +--------------------------------+
  | group:   obs:   first   second |
  |--------------------------------|
  |      1      1       1        a |
  |      1      6       1        a |
  |      2      5       2        b |
  |      2      7       2        b |
  +--------------------------------+

. duplicates drop first second, force  

Duplicates in terms of first second

(2 observations deleted)

. list 

     +------------------------------+
     | var1   var2   first   second |
     |------------------------------|
  1. |    a      1       1        a |
  2. |    a      2       2        a |
  3. |    a      3       3        a |
  4. |    b      1       1        b |
  5. |    b      2       2        b |
     +------------------------------+

. 输入str1（var1 var2）
var1 var2
1a 1
2a 2
三。a 3
4b 1
5b 2
61A
72 b
8结束
. genfirst=cond（var1）你可以接受这个答案来获得一些声誉。