Execution Phase (10)

Understanding DATA Step Processing

Execution Phase

Next, control returns to the top of the DATA step. Then the variable values in the program data vector are reset to missing. Notice that the automatic variables retain their values.

     data perm.update;
        infile invent;
        input Item $ 1-13 IDnum $ 15-19
              Instock 21-22 BackOrd 24-25;
        Total=instock+backord;
     run;

Raw Data File Invent

V---+----10---+----20---+-

Bird Feeder   LG088  3 20

6 Glass Mugs  SB082  6 12

Glass Tray    BQ049 12  6

Padded Hangrs MN256 15 20

Jewelry Box   AJ498 23  0

Red Apron     AQ072  9 12

Crystal Vase  AQ672 27  0

Picnic Basket LS930 21  0

Brass Clock   AN910  2 10

Control Returns to Top of DATA Step

SAS Data Set Perm.Update

Item IDnum InStock BackOrd Total

Bird Feeder LG088 3 20 23

Item	IDnum	InStock	BackOrd	Total
Bird Feeder	LG088	3	20	23

When reading raw data, SAS software sets the value of each variable in the DATA step to missing at the beginning of each iteration, with these exceptions:

variables named in a RETAIN statement
variables created in a sum statement
data elements in a _TEMPORARY_ array
any variables created with options in the FILE or INFILE statements
automatic variables.

In contrast, when reading a SAS data set, SAS software sets the values to missing only before the first iteration of the DATA step. Thereafter, the variables retain their values until new values become available, for example, through an assignment statement or through the next execution of a SET or MERGE statement. Variables created with options in the SET or MERGE statements also retain their values from one iteration to the next.