Extracting subset date from a timestamp date variable

[Fadzai Chikwava]

Dear Colleagues

Please help: I am trying to extract the first 8 characters (NEWdate) from a date format (OLDdate) which has timestamp in it.
OLDdate's format is %tc

OLDdate
14jan2011 00:00:00

NEWdate
14jan2011

I have tried the two commands below and they dont seem to work:

gen NEWdate = substr(OLDdate, 1, 9))
format NEWdate %td

gen NEWdate = dt(OLDdate_Date, 1, 9)
format NEWdate %td

Thanks for your help.

Regards

Fadzai

[Wouter Wakker]

If OLDdate is formatted %tc it's already a Stata datetime variable, which is in fact numeric rather than a string variable, which is why you cannot use string functions like substr(). A datetime variable contains the number of milliseconds since 1 January 1960.

Stata internal form (SIF) date/time variables have their own functions. To extract the date from a datetime variable you can use the dofc() function:

gen new_date = dofc(OLDdate)

I highly recommend to have a look at help datetime if you're planning on working more with date/time variables.

[William Lisowski]

This question was also asked, and answered with an example, at

https://www.statalist.org/forums/for...-date-variable