number-of-elements
is the number of variables in the group. You must enclose this value in either
parentheses (), braces {}, or brackets [].
$
specifies that the elements in the array are character elements.
length
specifies the length of the elements in the array that have not been previously
assigned a length.
array-elements
is a list of the names of the variables in the group. All variables that are defined in a
given array must be of the same type, either all character or all numeric.
initial-value-list
is a list of the initial values for the corresponding elements in the array.
For complete information, see the “ARRAY Statement” in SAS Statements: Reference.
To reference an array that was previously defined in the same DATA step, use an Array
Reference statement. An array reference has the following form:
array-name {subscript}
where
array-name
is the name of an array that was previously defined with an ARRAY statement in the
same DATA step.
subscript
specifies the subscript, which can be a numeric constant, the name of a variable
whose value is the number, a SAS numeric expression, or an asterisk (*).
Note: Subscripts in SAS are 1-based by default, and not 0-based as they are in some
other programming languages.
For complete information, see the Array Reference statement in the SAS Statements:
Reference.
Processing Simple Arrays
Grouping Variables in a Simple Array
The following ARRAY statement creates an array named Books that contains the three
variables Reference, Usage, and Introduction:
array books{3} Reference Usage Introduction;
When you define an array, SAS assigns each array element an array reference with the
form array-name{subscript}, where subscript is the position of the variable in the list.
The following table lists the array reference assignments for the previous ARRAY
statement:
558 Chapter 23 • Array Processing
Table 23.1 Array Reference Assignments for Array Books
Variable Array Reference
Reference books{1}
Usage books{2}
Introduction books{3}
Later in the DATA step, when you want to process the variables in the array, you can
refer to a variable by either its name or its array reference. For example, the names
Reference and Books{1} are equivalent.
Using a DO Loop to Repeat an Action
To perform the same action several times, use an iterative DO loop. A simple iterative
DO loop that processes an array has the following form:
DO index-variable=1 TO number-of-elements-in-array;
… more SAS statements …
END;
The loop is processed repeatedly (iterates) according to the instructions in the iterative
DO statement. The iterative DO statement contains an index-variable whose name you
specify and whose value changes at each iteration of the loop.
To execute the loop as many times as there are variables in the array, specify that the
values of index-variable are 1 TO number-of-elements-in-array. SAS increases the value
of index-variable by 1 before each new iteration of the loop. When the value exceeds the
number-of-elements-in-array, SAS stops processing the loop. By default, SAS
automatically includes index-variable in the output data set. Use a DROP statement or
the DROP= data set option to prevent the index variable from being written to your
output data set.
An iterative DO loop that executes three times and has an index variable named count
has the following form:
do count=1 to 3;
… more SAS statements …
end;
The first time that the loop processes, the value of count is 1; the second time, 2; and the
third time, 3. At the beginning of the fourth iteration, the value of count is 4, which
exceeds the specified range and causes SAS to stop processing the loop.
Using a DO Loop to Process Selected Elements in an Array
To process particular elements of an array, specify those elements as the range of the
iterative DO statement. For example, the following statement creates an array Days that
contains seven elements:
array days{7} D1-D7;
The following DO statements process selected elements of the array Days:
Processing Simple Arrays 559
Table 23.2 DO Statement Processing
DO Statement Description
do i=2 to 4;
processes elements 2 through 4
do i=1 to 7 by 2;
processes elements 1, 3, 5, and 7
do i=3,5;
processes elements 3 and 5
Selecting the Current Variable
You must tell SAS which variable in the array to use in each iteration of the loop. Recall
that you identify variables in an array by their array references and that you use a
variable name, a number, or an expression as the subscript of the reference. Therefore,
you can write programming statements so that the index variable of the DO loop is the
subscript of the array reference (for example, array-name{index-variable}). When the
value of the index variable changes, the subscript of the array reference (and therefore
the variable that is referenced) also changes.
The following example uses the index variable count as the subscript of array references
inside a DO loop:
array books{3} Reference Usage Introduction;
do count=1 to 3;
if books{count}=. then books{count}=0;
end;
When the value of count is 1, SAS reads the array reference as Books{1} and processes
the IF-THEN statement on Books{1}, which is the variable Reference. When count is 2,
SAS processes the statement on Books{2}, which is the variable Usage. When count is
3, SAS processes the statement on Books{3}, which is the variable Introduction.
The statements in the example tell SAS to
• perform the actions in the loop three times
• replace the array subscript count with the current value of count for each iteration of
the IF-THEN statement
• locate the variable with that array reference and process the IF-THEN statement on it
• replace missing values with zero if the condition is true.
The following DATA step defines the array Book and processes it with a DO loop.
options linesize=80 pagesize=60;
data changed(drop=count);
input Reference Usage Introduction;
array book{3} Reference Usage Introduction;
do count=1 to 3;
if book{count}=. then book{count}=0;
end;
datalines;
45 63 113
. 75 150
62 . 98
560 Chapter 23 • Array Processing
;
proc print data=changed;
title 'Number of Books Sold';
run;
The following output shows the CHANGED data set.
Output 23.1 Using an Array Statement to Process Missing Data Values
Defining the Number of Elements in an Array
When you define the number of elements in an array, you can either use an asterisk
enclosed in braces ({*}), brackets ([*]), or parentheses ((*)) to count the number of
elements or to specify the number of elements. You must list each array element if you
use the asterisk to designate the number of elements. In the following example, the array
C1Temp references five variables with temperature measures.
array c1temp{*} c1t1 c1t2 c1t3 c1t4 c1t5;
If you specify the number of elements explicitly, you can omit the names of the variables
or array elements in the ARRAY statement. SAS then creates variable names by
concatenating the array name with the numbers 1, 2, 3, and so on. If a variable name in
the series already exists, SAS uses that variable instead of creating a new one. In the
following example, the array c1t references five variables: c1t1, c1t2, c1t3, c1t4, and
c1t5.
array c1t{5};
Rules for Referencing Arrays
Before you make any references to an array, an ARRAY statement must appear in the
same DATA step that you used to create the array. Once you have created the array, you
can perform the following tasks:
• Use an array reference anywhere that you can write a SAS expression.
• Use an array reference as the arguments of some SAS functions.
• Use a subscript enclosed in braces, brackets, or parentheses to reference an array.
• Use the special array subscript asterisk (*) to refer to all variables in an array in an
INPUT or PUT statement or in the argument of a function.
Note: You cannot use the asterisk with _TEMPORARY_ arrays.
Processing Simple Arrays 561
..................Content has been hidden....................
You can't read the all page of ebook, please click here login for view all page.