The Power of RETAIN Statement in SAS Programming: Advantages and Use Cases

Author: Sarath

Date: October 10, 2024

Introduction

The RETAIN statement in SAS is a powerful tool used to control the behavior of variables across iterations in a data step. Unlike standard SAS variables, which are reset at the beginning of each iteration, RETAIN allows you to preserve the value of a variable from one iteration to the next. In this blog post, we will explore the advantages and use cases of the RETAIN statement in SAS programming, including controlling variable order, and provide practical examples.

Advantages of the RETAIN Statement

Preserve Values Across Iterations: The primary advantage of using the RETAIN statement is its ability to retain values across data step iterations. This feature is particularly useful when creating cumulative sums, counters, or when you need to remember values from a previous observation.
Improve Performance: The RETAIN statement can improve the efficiency of a program by eliminating the need for complex MERGE or PROC SQL steps. It simplifies the logic for tasks that require comparing current and previous observations.
Enhance Code Readability: By using RETAIN, you can avoid writing multiple lines of code to carry forward values. This makes your code cleaner and easier to understand.
Control Variable Order: The RETAIN statement allows you to explicitly specify the order in which variables appear in the output dataset. This is particularly useful when the default order (based on the order in which variables are created) does not meet your needs.

Common Use Cases of the RETAIN Statement

1. Cumulative Sums

The RETAIN statement is often used to calculate cumulative sums. For example, let's say you have a dataset with daily sales, and you want to calculate the total sales up to each day:

data cumulative_sales;
    set daily_sales;
    retain total_sales 0;
    total_sales = total_sales + sales;
run;

In this example, RETAIN ensures that the value of total_sales is carried forward from one observation to the next, allowing us to accumulate the total sales for each day.

2. Carry Forward Last Non-Missing Value

Another common use case is carrying forward the last non-missing value across observations. Here's an example where you want to carry the last valid value of a variable forward:

data carry_forward;
    set mydata;
    retain last_value;
    if not missing(value) then last_value = value;
run;

In this code, the RETAIN statement ensures that the variable last_value keeps its value until a new non-missing value is encountered.

3. Sequential Numbering or Counters

The RETAIN statement can also be used for counting occurrences or assigning sequential numbers to observations based on certain conditions:

data numbering;
    set events;
    retain event_count 0;
    if event = 'Yes' then event_count + 1;
run;

In this example, event_count increments by 1 whenever the event occurs, creating a sequential count of events.

4. Controlling Variable Order in the Output Dataset

In SAS, the default variable order in the output dataset is based on the order in which the variables are created. However, in some cases, you may want to control the order of the variables explicitly. The RETAIN statement allows you to achieve this. Here's an example:

data control_order;
    retain id name age salary; /* Specifying variable order */
    set employee_data;
    salary = salary * 1.1; /* Example of updating a variable */
run;

In this example, the RETAIN statement is used to specify the order in which the variables id, name, age, and salary will appear in the output dataset. Even though the salary variable is updated later in the data step, it will appear last in the specified order.

When to Use RETAIN vs. Other Methods

While the RETAIN statement is useful, there are other techniques such as FIRST. and LAST. variables, or MERGE with BY statements, that may serve similar purposes. However, RETAIN is generally more efficient for simple tasks such as accumulating values, counting, or controlling variable order.

Conclusion

The RETAIN statement is a valuable feature in SAS programming that can simplify your code and improve efficiency. Whether you're calculating cumulative sums, carrying forward non-missing values, creating counters, or controlling variable order, understanding how to use RETAIN will help you develop more effective SAS programs. Incorporate it wisely into your data steps to optimize your workflows!