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GENERAL GUIDELINES:
Windows in SAS
File management

The SAS Program
Program syntax
Debugging tips

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 USING SAS PROGRAMMING TO: 
   

1. Prepare the data set 
   Types of data 
   Example programs    
    
2. View the data
   SAS Procedures
  
3. Explore the data  
   Numeric statistics    
   Frequency tables    
    
4. Manipulate the data  
   Basic techniques    
   New variables
  
5. Adding Variables and 
Observations to Data Sets
   The SET Statement
   The MERGE Statement

6. Data Processing
   ARRAY Statement
   Do Loops
   By-Group Processing
   RETAIN Statement

  
NON-PROGRAMMING 
      Alternatives

 
SAMPLE DATA SETS: 
 Height/weight
 Height/weight/region
 Simulated clinical data 
 Simulated Manitoba Health 
    

Purpose We can often do data calculations/manipulations within observations, but sometimes it is necessary to do calculations across observations. The RETAIN statement is used to keep a specified value (assigned by an INPUT or assignment statement) from the current iteration of the DATA step to the next. Otherwise, SAS automatically sets such values to missing before each iteration of the DATA step. The RETAIN statement allows values to be kept across observations; for example, computing a running total of values, counting the number of occurrences of a variable's value, setting indicators within a BY-group, and so on. RETAIN statements are often used with FIRST. and LAST. processing. Syntax The RETAIN statement can be used to specify initial values for variable(s) or elements of an array. All elements or variables will be initialized to the specified value. RETAIN <varlist> [initial-value(s)]; Varlist: specifies the names of the variables, lists or arrays whose values you wish to retain. Initial-value(s): the initial value(s) can be numeric or character (e.g., 'y') and is assigned to all listed variables. If the initial value is not specified, it is set to missing. The following shows four variables specified in each retain statement. RETAIN var1-var4 1; sets initial values of var1, var2, var3, var4 to 1. RETAIN var1-var4 (1); only var1 is set to 1; var2-4 are set to missing. RETAIN var1-var4 (1 2 3 4); OR RETAIN var1-var4 (1,2,3,4); var1 is set to 1, var2 to 2, var3 to 3, var4 to 4. For example, the statement RETAIN pop 1; within a DATA step will assign a value of 1 to each observation for the variable POP. /*Use the retain statement to count the number of observations in each BY group. An index weight is identified and each subsequent weight is compared to the index. An example is given for how the output might look*/ PROC SORT data=htwt_long; by name age; run; data w_compare (keep=name age index_weight weight over count last_name) set htwt_long; by name; retain count index_weight; if first.name then do; count=0; /*Set and retain the first weight*/ index_weight=weight; end; /*Counter for number of records for each*/ count=count+1; /*Indicator variable for increased weight*/ over = (index_weight < weight); last_name=last.name; run; PROC PRINT data=w_compare; var name age weight over index_weight weight count; title 'Retain Statement'; run; PRACTICE QUESTIONS ON DATA PROCESSING The following two questions assume that a permanent SAS data set has been created from the sample clinical data, including the format file. Examples are given for how program, log and output might look. 1. Create a BY-group by primary DX. 2. Count the number of observations in each BY-group using the RETAIN statement. The following questions assume that a permanent SAS data set has been created from the simulated Manitoba health data available at MCHP. Examples are given for how program, log and output might look. 3. Use the ARRAY statement to find all the records with a diabetes diagnosis (code 250). Hint: the SUBSTR function is useful here.   Home VIc. Data Processing: By-Group Processing (First./Last.) NEXT Non-Programming Alternatives