如何利用preserve或者snapshot去merge

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我在整理数据时希望在不保存之前合并的数据到硬盘的情况下，也就是仅利用闪存存储master数据，继续与新的数据集合并。求问大神应该咋做？我感觉可以利用preserve和snapshot做，但是不知道这两个命令具体咋用咋操作的。先谢谢了！

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关键词：preserve Snapshot Reserve Serve Merge

我猜测可能可以用 tempfile！

1. * Example generated by -dataex-. To install: ssc install dataex
   
2. clear
   
3. input float date str4 id
   
4. 20068 "rd5"
   
5. 20115 "rd6"
   
6. 20116 "rd7"
   
7. 20123 "rd8"
   
8. 20124 "rd8"
   
9. 20124 "rd7"
   
10. 20124 "rd5"
    
11. end
    
12. format %td date
    
13. tempfile base
    
14. save `base'
    
15. 
    
16. * Example generated by -dataex-. To install: ssc install dataex
    
17. clear
    
18. input float(date rd12 rd7 rd8)
    
19. 20068 7 5 2
    
20. 20115 2 6 3
    
21. 20116 1 7 4
    
22. 20123 6 8 5
    
23. 20124 7 9 6
    
24. 20124 7 9 6
    
25. 20124 7 9 6
    
26. end
    
27. format %td date
    
28. //    GET RID OF DUPLICATE OBSERVATIONS
    
29. duplicates drop
    
30. tempfile merge1
    
31. save `merge1'
    
32. 
    
33. * Example generated by -dataex-. To install: ssc install dataex
    
34. clear
    
35. input float(date rd5 rd6 rd99)
    
36. 20068 5 1 9
    
37. 20115 4 4 7
    
38. 20116 3 5 6
    
39. 20123 8 2 1
    
40. 20124 3 7 2
    
41. 20124 3 7 2
    
42. 20124 3 7 2
    
43. end
    
44. format %td date
    
45. //    AGAIN, ELIMINATE DUPLICATE OBSERVATIONS
    
46. duplicates drop
    
47. tempfile merge2
    
48. save `merge2'
    
49. 
    
50. //    BRING IN THE BASE DATA AND IDENTIFY THE VARIABLES NEEDED
    
51. use `base', clear
    
52. levelsof id, local(needed)
    
53. 
    
54. //    IDENTIFY ALL VARIABLES IN THE MERGE1 DATA
    
55. des using `merge1', varlist
    
56. local vbles `r(varlist)'
    
57. //    AND PICK OUT THE ONES THAT ARE MENTIONED IN id IN THE BASE DATA
    
58. local keepers: list needed & vbles
    
59. //    MERGE, RETAINING ONLY THOSE VARIABLES
    
60. merge m:1 date using `merge1', keepusing(`keepers') gen(merge1)
    
61. 
    
62. //    DO THE SAME WITH THE MERGE2 DATA SET
    
63. des using `merge2', varlist
    
64. local vbles `r(varlist)'
    
65. local keepers: list needed & vbles
    
66. merge m:1 date using `merge2', keepusing(`keepers') gen(merge2)
    
67. order merge*, last

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