SAS 9.4 Language Reference, 6th Edition

Dropping, Keeping, and Renaming Variables

Using Statements or Data Set Options

The DROP, KEEP, and RENAME statements or the DROP=, KEEP=, and RENAME=

data set options control which variables are processed or output during the DATA step.

You can use one or a combination of these statements and data set options to achieve the

results that you want. The action taken by SAS depends largely on whether you perform

one of the following actions:

• Use a statement or data set option or both.

• Specify the data set options on an input or an output data set.

The following table summarizes the general differences between the DROP, KEEP, and

RENAME statements and the DROP=, KEEP=, and RENAME= data set options.

Table 4.6 Statements versus Data Set Options for Dropping, Keeping, and Renaming

Variables

Statements Data Set Options

apply to output data sets only apply to output or input data sets

affect all output data sets affect individual data sets

can be used in DATA steps only can be used in DATA steps and PROC steps

can appear anywhere in DATA steps must immediately follow the name of each

data set to which they apply

Using the Input or Output Data Set

You must also consider whether you want to drop, keep, or rename the variable before it

is read into the program data vector or as it is written to the new SAS data set. If you use

the DROP, KEEP, or RENAME statement, the action always occurs as the variables are

written to the output data set. With SAS data set options, where you use the option

determines when the action occurs. If the option is used on an input data set, the variable

is dropped, kept, or renamed before it is read into the program data vector. If used on an

output data set, the data set option is applied as the variable is written to the new SAS

data set. (In the DATA step, an input data set is one that is specified in a SET, MERGE,

or UPDATE statement. An output data set is one that is specified in the DATA

statement.) Consider the following facts when you make your decision:

• If variables are not written to the output data set and they do not require any

processing, using an input data set option to exclude them from the DATA step is

more efficient.

• If you want to rename a variable before processing it in a DATA step, you must use

the RENAME= data set option in the input data set.

Dropping, Keeping, and Renaming Variables 53

• If the action applies to output data sets, you can use either a statement or a data set

option in the output data set.

The following table summarizes the action of data set options and statements when they

are specified for input and output data sets. The last column of the table tells whether the

variable is available for processing in the DATA step. If you want to rename the variable,

use the information in the last column.

Table 4.7 Status of Variables and Variable Names When Dropping, Keeping, and Renaming

Variables

Where

Specified

Data Set Option or

Statement Purpose

Status of Variable

or Variable Name

Input data set DROP=

KEEP=

includes or excludes

variables from processing

if excluded,

variables are not

available for use in

DATA step

RENAME= changes name of variable

before processing

use new name in

program statements

and output data set

options; use old

name in other input

data set options

Output data set DROP, KEEP specifies which variables are

written to all output data sets

all variables

available for

processing

RENAME changes name of variables

in all output data sets

use old name in

program

statements; use new

name in output data

set options

DROP=

KEEP=

specifies which variables are

written to individual output

data sets

all variables are

available for

processing

RENAME= changes name of variables

in individual output data sets

use old name in

program statements

and other output

data set options

Order of Application

If your program requires that you use more than one data set option or a combination of

data set options and statements, it is helpful to know that SAS drops, keeps, and renames

variables in the following order:

• First, options on input data sets are evaluated left to right within SET, MERGE, and

UPDATE statements. DROP= and KEEP= options are applied before the

RENAME= option.

• Next, DROP and KEEP statements are applied, followed by the RENAME

statement.

54 Chapter 4 • SAS Variables