Filtering out fourth quarter observations

[Ralph Klijn]

Hello everybody,

I have a panel data set with quarterly data. The time data is reported in the following manner:


19900331
19900630
19900930
19901231
19910331
19910630
19910930
19911231
19920331

The only observations I am interested in are the fourth quarter observations. Therefore, if my dataset was limited to the points in time described above, I wanted to only keep:

19901231
19911231

How do I do this?

Thank you in advance and best regards,

[Nick Cox]

As in your other thread it is not clear exactly how your dates are held but in Stata there is no practical solution except to follow Stata rules for handling dates like these. help datetime is essential reading.

I am guessing that your dates are just large integers. This shows some technique.

clear
input long problemdate 
19900331
19900630
19900930
19901231
19910331
19910630
19910930
19911231
19920331
end 

gen dailydate = daily(string(problemdate, "%8.0f"), "YMD")
gen qdate = qofd(dailydate) 
gen quarter = quarter(dailydate)
format qdate %tq 
format dailydate %td 

list , sep(4) 

     +-----------------------------------------+
     | proble~e   dailydate    qdate   quarter |
     |-----------------------------------------|
  1. | 19900331   31mar1990   1990q1         1 |
  2. | 19900630   30jun1990   1990q2         2 |
  3. | 19900930   30sep1990   1990q3         3 |
  4. | 19901231   31dec1990   1990q4         4 |
     |-----------------------------------------|
  5. | 19910331   31mar1991   1991q1         1 |
  6. | 19910630   30jun1991   1991q2         2 |
  7. | 19910930   30sep1991   1991q3         3 |
  8. | 19911231   31dec1991   1991q4         4 |
     |-----------------------------------------|
  9. | 19920331   31mar1992   1992q1         1 |
     +-----------------------------------------+

If I have guessed right

keep if quarter == 4

is what you want.

[Ralph Klijn]

Thank you very much Nick. Is it possible as well to convert date variables such as 'qdate' to a variable indicating which quarter it is, in this case 'quarter'? Thank you in advance.

[Nick Cox]

Code in #2 does precisely that, so I can't see a different question.