st: dates in the 'if' condition

[Tomas.Konecny@cnb.cz]

Hi,
I have not used Stata in time-series context before and would like to ask
a rather simple thing. Having the time variable in a %tq format, it displays the date label but the underlying value
is a number. I have tried to condition with the `if' statement referring to the label instead of the underlying value, but to no avail. Is there any way to do so?
Here is an example:
              storage  display     value
variable name   type   format      label      variable label
--------------------------------------------------------------------------------------------------------------------------------------
time          float  %tq                    

keep if time==1997q4
1997q4 invalid name
r(198);

keep if time=="1997q4"
type mismatch
r(109);

Thank you,
Tomas 

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