Extracting Monthly Date from String with Multiple Daily Date Formats

[Maxence Morlet]

Hi all,

input str11 startdate2
"Apr 1 1997"
"Apr 1 1997"
"Apr 1 1999"
"Apr 1 1999"
"Apr 1 1999"
"Apr 1 2000"
"Apr 1 2000"
"Apr 1 2000"
"Jul 1 2001"
"Jul 1 2001"
"Jul 1 2001"
"Jul 1 2001"
"Jul 1 2001"
"Jun 1 2002"
"Jun 1 2002"
"Jun 1 2002"
"Jun 1 2003"
"23-Jun-10"
"23-Jun-14"
"23-May-11"
"23-Nov-13"
"23-Oct-14"

I have a dataset with this date variable, which is a string. It is a very weird variable, as the daily date is shown in two different formats: MMM D YYYY and DD-MMM-YY.

I would like to extract the monthly date from all observations of this variable, i.e. for both date formats.

I tried the very helpful code of Nick Cox in the following post: https://www.statalist.org/forums/for...rom-a-date-var and the user-written numdate command (from SSC), however I only got missing values generated.

Please could someone let me know how to extract a monthly date out of this variable?

[Nick Cox]

I would get a daily date first, as otherwise you just have to ignore the day part in two different ways.

clear 
input str11 startdate2
"Apr 1 1997"
"Apr 1 1997"
"Apr 1 1999"
"Apr 1 1999"
"Apr 1 1999"
"Apr 1 2000"
"Apr 1 2000"
"Apr 1 2000"
"Jul 1 2001"
"Jul 1 2001"
"Jul 1 2001"
"Jul 1 2001"
"Jul 1 2001"
"Jun 1 2002"
"Jun 1 2002"
"Jun 1 2002"
"Jun 1 2003"
"23-Jun-10"
"23-Jun-14"
"23-May-11"
"23-Nov-13"
"23-Oct-14"
end 

duplicates drop 
gen wanted = daily(startdate2, "MDY")
replace wanted = daily(startdate2, "DM20Y") if missing(wanted)
sort wanted 
format wanted %td 
list 

     +------------------------+
     | startdate2      wanted |
     |------------------------|
  1. | Apr 1 1997   01apr1997 |
  2. | Apr 1 1999   01apr1999 |
  3. | Apr 1 2000   01apr2000 |
  4. | Jul 1 2001   01jul2001 |
  5. | Jun 1 2002   01jun2002 |
     |------------------------|
  6. | Jun 1 2003   01jun2003 |
  7. |  23-Jun-10   23jun2010 |
  8. |  23-May-11   23may2011 |
  9. |  23-Nov-13   23nov2013 |
 10. |  23-Jun-14   23jun2014 |
     |------------------------|
 11. |  23-Oct-14   23oct2014 |
     +------------------------+

Now it's just

replace wanted = mofd(wanted)

[Maxence Morlet]

Thank you very much! It worked a wonder