How Does a RETAIN Statement Work in SAS?

In SAS, the RETAIN statement is a powerful tool used to control the retention of variable values across iterations of the DATA step. Unlike default behavior where SAS initializes variable values to missing at the start of each iteration, the RETAIN statement allows you to specify that certain variables should retain their values from one iteration to the next.

How RETAIN Works

Syntax

The RETAIN statement is placed before the DATA step processes the data. It can be used to list one or more variables whose values you wish to retain. The syntax is as follows:

DATA new_dataset;    RETAIN variable1 variable2;    / Other statements /RUN

Retention of Values

When a variable is specified in the RETAIN statement, its value is maintained across iterations. This means that during the next iteration of the DATA step, the variable will not be reset to missing; instead, it retains the last value assigned to it.

Initialization

You can also initialize a retained variable to a specific value. If you do not initialize it the first time it is referenced, it will have a missing value.

Here's an example to illustrate the use of the RETAIN statement:

DATA example;    RETAIN total 0; /* Initialize total to 0 and retain its value */    input value;    total total   value; /* Accumulate the sum of value into total */    datalines:102030;RUNPROC PRINT DATAexample;RUN

Explanation of the Example

In this example, we create a dataset called example. The RETAIN statement is used to keep the value of total across iterations. The line total total value is a shorthand for accumulating the sum of value into total. Each time a new value is read, it is added to the existing total.

When you print the dataset, you will see how total accumulates the sum of value over the iterations.

Use Cases

Cumulative Sums

As shown in the example, the RETAIN statement is commonly used for cumulative calculations. It is particularly useful for creating running totals or sums of values across multiple observations.

Flags or Indicators

The RETAIN statement can also be used to carry forward flags or indicators from one observation to the next. This is particularly useful in scenarios where you need to maintain a state across multiple rows or iterations.

Data Transformation

The RETAIN statement is also useful in data transformations where you need to maintain state information across rows. For instance, you might want to update a variable based on the cumulative sum of another variable in a dataset.

Important Notes

It is important to note that the RETAIN statement does not affect how the data is read; it only affects how variable values are stored and maintained within the DATA step.

If you want to reset the value of a retained variable based on certain conditions, you can do so within the DATA step logic. This flexibility allows you to manage the flow of data manipulation in SAS, especially in more complex data processing tasks.