Understanding DATA Step Processing (3)

Debugging and Testing DATA Steps

Understanding DATA Step Processing

When the SET statement is compiled, a slot is added to the program data vector for each variable in the input data set. The input data set supplies the variable names and attributes such as type and length.

     data finance.duejan;
        set finance.loans;
        Interest=amount*(rate/12);
     run;

SAS Data Set Finance.Loans

Account Amount Rate Months Payment

101-1092 22000 0.1000 60 467.43

101-1731 114000 0.0950 360 958.57

101-1289 10000 0.1050 36 325.02

101-3144 3500 0.1050 12 308.52

Account	Amount	Rate	Months	Payment
101-1092	22000	0.1000	60	467.43
101-1731	114000	0.0950	360	958.57
101-1289	10000	0.1050	36	325.02
101-3144	3500	0.1050	12	308.52

Program Data Vector with automatic variables

Any variables created in the DATA step are also added to the program data vector. For example, the assignment statement below creates the variable Interest. As the statement is compiled, the variable is added to the program data vector. The attributes of Interest are determined by the expression in the statement. Because the expression produces a numeric value, Interest is defined as a numeric variable and assigned a default length of 8.

data finance.duejan; set finance.loans; Interest=amount*(rate/12); run;

Programmed variables added to PDV

At the bottom of the DATA step (in this example, when the RUN statement is encountered), the compilation phase is complete and the descriptor portion of the new SAS data set is created. The descriptor portion of the data set includes:

name of the data set
number of observations and variables
names and attributes of the variables.

Description of Finance.Duejan

Observations: 0
Variables: 6

Variable Type Length

Account CHAR 8

Amount NUM 8

Rate NUM 8

Months NUM 8

Payment NUM 8

Interest NUM 8

At this point, the data set contains the six variables defined in the input data set and assignment statement. Remember, _N_ and _ERROR_ are not written to the data set. There are no observations because the DATA step has not yet executed.