[Leonardo Guizzetti]

Rana, please pay attention to the new variable that you just created, called -country_id-, and then using a different variable name when defining the condition, -country_code-. This was the typo I referred to.

Using -encode- turns your string variable country into a labelled, numeric variable (you've already made it and called it -country_id-) on Carlo's suggestion. The following code will select all countries that are not in the mentioned list, and then drop them, which with your data example, results in an empty dataset.

gen wanted=1 if !inlist(country_id, 20, 63, 179)
drop if wanted

You will need to ensure that the countries are correctly selected.

[Carlo Lazzaro]

Rana:
provided that Leonardo's solution is more elegant, elabiorating a bit on what we all shared in this thread you can end up with something similar:

. encode country,gen(country_id)

. label list
country_id:
           1 Afghanistan
           2 Africa (total)
           3 Albania
           4 Algeria
           5 America (total)
           6 Andorra
           7 Angola

. gen wanted=1 if country_id!=1 & country_id!=3 & country_id!=4
(46 missing values generated)

. replace wanted=0 if wanted==.
(46 real changes made)

. drop if wanted==1
(54 observations deleted)

. list

     +------------------------------------------------------------------------------+
     |     country     mdate   n_cases   n_deaths   countr~e    country_id   wanted |
     |------------------------------------------------------------------------------|
  1. | Afghanistan    2020m1         0          0        AFG   Afghanistan        0 |
  2. | Afghanistan    2020m2         1          0        AFG   Afghanistan        0 |
  3. | Afghanistan    2020m3       113          4        AFG   Afghanistan        0 |
  4. | Afghanistan    2020m4      2590         81        AFG   Afghanistan        0 |
  5. | Afghanistan    2020m5     12501        172        AFG   Afghanistan        0 |
     |------------------------------------------------------------------------------|
  6. | Afghanistan    2020m6     15762        464        AFG   Afghanistan        0 |
  7. | Afghanistan    2020m7      5743        563        AFG   Afghanistan        0 |
  8. | Afghanistan    2020m8      1452        118        AFG   Afghanistan        0 |
  9. | Afghanistan    2020m9      1179         60        AFG   Afghanistan        0 |
 10. | Afghanistan   2020m10      2292         79        AFG   Afghanistan        0 |
     |------------------------------------------------------------------------------|
 11. | Afghanistan   2020m11      4211        222        AFG   Afghanistan        0 |
 12. | Afghanistan   2020m12      7065        467        AFG   Afghanistan        0 |
 13. | Afghanistan    2021m1      2450        183        AFG   Afghanistan        0 |
 14. | Afghanistan    2021m2       517         38        AFG   Afghanistan        0 |
 15. | Afghanistan    2021m3       903         61        AFG   Afghanistan        0 |
     |------------------------------------------------------------------------------|
 16. | Afghanistan    2021m4      5063        174        AFG   Afghanistan        0 |
 17. |     Albania    2020m3       212         10        ALB       Albania        0 |
 18. |     Albania    2020m4       583         21        ALB       Albania        0 |
 19. |     Albania    2020m5       342          2        ALB       Albania        0 |
 20. |     Albania    2020m6      1265         22        ALB       Albania        0 |
     |------------------------------------------------------------------------------|
 21. |     Albania    2020m7      3117        111        ALB       Albania        0 |
 22. |     Albania    2020m8      3861        114        ALB       Albania        0 |
 23. |     Albania    2020m9      4886        116        ALB       Albania        0 |
 24. |     Albania   2020m10      6936        122        ALB       Albania        0 |
 25. |     Albania   2020m11     16423        280        ALB       Albania        0 |
     |------------------------------------------------------------------------------|
 26. |     Albania   2020m12     21813        395        ALB       Albania        0 |
 27. |     Albania    2021m1     25898        267        ALB       Albania        0 |
 28. |     Albania    2021m2     27561        479        ALB       Albania        0 |
 29. |     Albania    2021m3     13634        326        ALB       Albania        0 |
 30. |     Albania    2021m4      5192        147        ALB       Albania        0 |
     |------------------------------------------------------------------------------|
 31. |     Algeria    2020m1         0          0        DZA       Algeria        0 |
 32. |     Algeria    2020m2         3          0        DZA       Algeria        0 |
 33. |     Algeria    2020m3       508         31        DZA       Algeria        0 |
 34. |     Algeria    2020m4      3963        432        DZA       Algeria        0 |
 35. |     Algeria    2020m5      4920        190        DZA       Algeria        0 |
     |------------------------------------------------------------------------------|
 36. |     Algeria    2020m6      3879        244        DZA       Algeria        0 |
 37. |     Algeria    2020m7     18192        334        DZA       Algeria        0 |
 38. |     Algeria    2020m8     12681        270        DZA       Algeria        0 |
 39. |     Algeria    2020m9      7990        259        DZA       Algeria        0 |
 40. |     Algeria   2020m10      6136        213        DZA       Algeria        0 |
     |------------------------------------------------------------------------------|
 41. |     Algeria   2020m11     23949        437        DZA       Algeria        0 |
 42. |     Algeria   2020m12     18187        362        DZA       Algeria        0 |
 43. |     Algeria    2021m1      8680        142        DZA       Algeria        0 |
 44. |     Algeria    2021m2      5294        104        DZA       Algeria        0 |
 45. |     Algeria    2021m3      3357         90        DZA       Algeria        0 |
     |------------------------------------------------------------------------------|
 46. |     Algeria    2021m4      6365        220        DZA       Algeria        0 |
     +------------------------------------------------------------------------------+

.

Leonardo's wise advice about double-checking the number each country refers to still applies.