Generating Dummy Variables for dates

[Peter John]

I'm currently trying to create dummy variables using dates (my date variable is currently in %td format), I want to certain a dummy for certain time period with a set start and end date. Additionally, I want to split my dates into month, quarter and year to help me merge with other data which only has a monthly, quarterly and yearly frequency. If anyone can help me with this I would appreciate it.

[Andrew Musau]

The following is illustrative:

sysuse sp500, clear
keep in 1/20
g wanted= inrange(date, td(05jan2001), td(20jan2001))
foreach var in month quarter year{
    g `var'= `var'(date)
}

In general, see

h datetime
h inrange()

Res.:

. l date wanted-year, sep(0)

     +---------------------------------------------+
     |      date   wanted   month   quarter   year |
     |---------------------------------------------|
  1. | 02jan2001        0       1         1   2001 |
  2. | 03jan2001        0       1         1   2001 |
  3. | 04jan2001        0       1         1   2001 |
  4. | 05jan2001        1       1         1   2001 |
  5. | 08jan2001        1       1         1   2001 |
  6. | 09jan2001        1       1         1   2001 |
  7. | 10jan2001        1       1         1   2001 |
  8. | 11jan2001        1       1         1   2001 |
  9. | 12jan2001        1       1         1   2001 |
 10. | 16jan2001        1       1         1   2001 |
 11. | 17jan2001        1       1         1   2001 |
 12. | 18jan2001        1       1         1   2001 |
 13. | 19jan2001        1       1         1   2001 |
 14. | 22jan2001        0       1         1   2001 |
 15. | 23jan2001        0       1         1   2001 |
 16. | 24jan2001        0       1         1   2001 |
 17. | 25jan2001        0       1         1   2001 |
 18. | 26jan2001        0       1         1   2001 |
 19. | 29jan2001        0       1         1   2001 |
 20. | 30jan2001        0       1         1   2001 |
     +---------------------------------------------+

[Peter John]

I found a different simpler way to split it into month, year and quarter using:

gen year = year(new_date)
gen month = month(new_date)
gen quarter = quarter(new_date)

Appreciate your help anyway.

[Andrew Musau]

This

gen year = year(new_date)
gen month = month(new_date)
gen quarter = quarter(new_date)
.

and

foreach var in month quarter year{
g `var'= `var'(date)
}

are equivalent, although I agree that a loop may look daunting if you haven't encountered it before. See

help foreach

for an introduction to looping.

[Peter John]

Thanks for this, I have to admit I didn't understand the loop in the previous post, I'll give it a try now.

[Peter John]

So in my case, my date variable in named 'new_date' so I'd replace date in that script with 'new_date'. So is var the month, quarter and year variables?

[Andrew Musau]

There is some kind of repetition here:

gen year = year(new_date)
gen month = month(new_date)
gen quarter = quarter(new_date)

In a loop

foreach var in year month quarter{
    gen `var'= `var'(new_date)
}

In the first iteration, `var' is year, second, month and final, quarter.

[Peter John]

Thank you, that is a lot easier to understand now.