SAS Tip
of the Month I was asked a short time ago why use the SAS SUM function when adding two numbers a simple arithmetic expression is possible? To give a simple answer it is the way SAS deals with a 'missing' value. To use an example the following timesheet data for a project is loaded using the following datastep and two variable TOT_SUM and TOT_ARITH are created: data TimeSheet; infile cards; input DAY $ 13 AM_HOURS 58 PM_HOURS 1013; TOT_SUM=sum(AM_HOURS,PM_HOURS); TOT_ARITH=AM_HOURS+PM_HOURS; cards; .... The variable TOT_SUM is created from adding the variables AM_Hours and PM_Hours using the SUM function while the variable TOT_ARITH is created from the using an arithmetic expression. The following table shows the results: DATASET:TimeSheet Day AM_Hours PM_Hours Tot_Sum Tot_Arith  MON 3.5 4.5 8.0 8.0 TUE . 1.0 1.0 . WED 2.5 . 2.5 . THU . . . . FRI 2.0 3.0 5.0 5.0 From the table the variable TOT_SUM is correct as it considers the 'missing' value as a valid value in the expression. Have a safe and happy holiday season. 

________________________________ Updated December 6, 2004 