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Time Shifting

INTNX is a very useful SAS date function which returns a SAS date corresponding to a point within a time interval either in the past or the future. The general syntax of the INTNX function is:

Date_Variable = INTNX("interval",start_date,increment);

Intervals typically used with INTNX include WEEK, MONTH, QTR (quarter) and YEAR, and the function will return the start of the requested interval, e.g. weeks always begin on a Sunday and years on the 1st January.

It is not uncommon that the default starting points don't quite meet our needs. We can use a "shift index" in the interval specification to request an alternative starting point is used. For example the interval "WEEK.2" requests weeks which start on a Monday and "YEAR.11" requests years which start on the 1st November.

Here are a few examples using this technique:

data _null_; today = "10DEC2010"d;
  Next_Tuesday = INTNX("WEEK.3",today,1);
  Next_April_Fools = INTNX("YEAR.4",today,1);
 
put "The next Tuesday is: " Next_Tuesday date9.; put "The next April Fools Day is: " Next_April_Fools date9.; run;

The following is output to the SAS log:

The next Tuesday is: 14DEC2010
The next April Fools Day is: 01APR2011

For more information please consult the SAS Help documentation.