How to create new variable with month and year since May, 2011 as n°1

[Jean-Baptiste Lascarrou]

Dear Statalister,

I'm trying to create a new variable derived from one date (DateACR_num) which include month and date reformated as 1,2,3 from May 2011 (=1).

I try:

gen date = dofm(DateACR_num)
format date %tm
gen wanted = date - ym(2011, 05)

But results are no relevant

* Example generated by -dataex-. To install: ssc install dataex
clear
input float(DateACR_num wanted)
18763 570470
18763 570470
18765 570531
18765 570531
18766 570562
18766 570562
18767 570592
18767 570592
18767 570592
18767 570592
18767 570592
18767 570592
18767 570592
18768 570623
18770 570683
18771 570714
18772 570744
18773 570775

[Nick Cox]

Thanks for the data example. Your DateACR_num is evidently a daily date variable. That being so, pushing it through dofm() makes no sense. dofm() is for converting monthly dates to daily dates. You want the other way round, I think.

clear
input float(DateACR_num wanted)
18763 570470
18763 570470
18765 570531
18765 570531
18766 570562
18766 570562
18767 570592
18767 570592
18767 570592
18767 570592
18767 570592
18767 570592
18767 570592
18768 570623
18770 570683
18771 570714
18772 570744
18773 570775
end 

format %td DateACR_num 

gen Wanted = mofd(DateACR_num) - ym(2011, 5) 

list, sepby(Wanted) 

     +-----------------------------+
     | DateACR~m   wanted   Wanted |
     |-----------------------------|
  1. | 16may2011   570470        0 |
  2. | 16may2011   570470        0 |
  3. | 18may2011   570531        0 |
  4. | 18may2011   570531        0 |
  5. | 19may2011   570562        0 |
  6. | 19may2011   570562        0 |
  7. | 20may2011   570592        0 |
  8. | 20may2011   570592        0 |
  9. | 20may2011   570592        0 |
 10. | 20may2011   570592        0 |
 11. | 20may2011   570592        0 |
 12. | 20may2011   570592        0 |
 13. | 20may2011   570592        0 |
 14. | 21may2011   570623        0 |
 15. | 23may2011   570683        0 |
 16. | 24may2011   570714        0 |
 17. | 25may2011   570744        0 |
 18. | 26may2011   570775        0 |
     +-----------------------------+

[Maarten Buis]

gen date = dofm(DateACR_num)
format DateACR_num %td
gen wanted = mofd(DateACR_num) // measure time in months rather than days
gen wanted = wanted - ym(2011, 05) // center at May 2011

[Jean-Baptiste Lascarrou]

Thanks to both.

It works well.

Have a nice day.