SAS arrays: What are they and why use them?

What is a SAS array?

• a set of variables grouped together for the duration of a data step by being given a name in an ARRAY statement

       array pop(1:5) ga sc nc va wv;

  • array name is "pop"
  • the sequence of variable names ga sc nc va wv is the "array list"
  • the variables in the array list are the "array elements"
  • each array element in this example has a position number in the array list from 1 to 5

Convenience of arrays

• two ways to refer to variables which are array elements
  • variable name
  • array name with subscript pointing to position of variable in the array list

      pop(3) refers to the variable in position number 3 in the array pop (nc in above example)

Subscripts can be

• constants
• variables
• expressions

Array elements

• must all be of same type (numeric or character)
• can be variables which exist or which will be created in the data step

One-dimensional array declarations

  array x(1:6) a b c d e f;            * x(5) is the variable e *;
                                       * subscript lower bound= 1 : upper bound= 6 *;

  array x(0:5) a b c d e f;            * x(4) is the variable e *;

  array quiz(20) q1-q20;               * equivalent array declarations *;
  array quiz(1:20) q1-q20;             * quiz(4) is the variable q4 *;
                                       
  array quiz(*) q1-q20;                * use an asterisk and have SAS figure out how many variables 
                                       *  there are in the array *;
 
  array quiz(20);                      * SAS creates quiz1-quiz20 as array elements *;
 
  array color(1:3) $1 red blue green;  * character array, elements have length= 1 character *;
                                       * color(2) is the variable blue *;

  array pop(1:5) yr95-yr99;            * pop(2) is the variable yr96 *;

  array pop(95:99) yr95-yr99;          * pop(96) is the variable yr96 *;

  array x(*) _numeric_;                * all numeric variables on the observation *;
  array y(*) _character_;              * all character variables on the observation *;

Two-dimensional array declarations

array quiz(1:4, 1:5) q1-q20;  
   /**   picture 4 rows, 5 columns: 
             q1  q2  q3  q4  q5
             q6  q7  q8  q9  q10
             q11 q12 q13 q14 q15
             q16 q17 q18 q19 q20 
                                   
             q(2,4) is the variable q9 **/

array pop(1:3, 98:99) nc98 nc99 va98 va99 sc98 sc99;  
   /**   picture 3 rows, 2 columns:
             nc98  nc99
             va98  va99
             sc98  sc99

             pop(3,99) is the variable sc99 **/

Why use SAS arrays?

• repeat an action or set of actions on each of a group of variables
• write shorter programs
• restructure a SAS data set to change the unit of observation

Simple examples using one-dimensional arrays

     array v(7) a b c d e f g;

     * this creates a permanent variable named k: *;
     do k= 1 to 7;
       if v(k) = 99 then v(k)= .;
     end;

2. Each observation of your data set has five variables:  SEX1 SEX2 SEX3 SEX4 SEX5 which give the sex (1= male, 2= female) of up to 5 persons. You want to count the number of males (MALES) and the number of females (FEMALES) on each observation.

     array sex(1:5) sex1-sex5;

     males= 0;
     females= 0;
     do i= 1 to 5;
       if sex(i) = 1 then males= males + 1;
        else if sex(i) = 2 then females= females + 1;
     end;

3. Recode all numeric variables in your data set as follows: if a variable has a value of 98 or 99 recode it to SAS missing.

     array nvar(*) _numeric_;

     do i= 1 to dim(nvar);  
       if nvar(i) in(98, 99) then nvar(i)= .;
     end;

Using arrays to restructure a SAS data set