Choosing Rows and Columns

Prerequisites: Conditional logic

Most DATA steps start from an existing data set with SET and keep only what you need.

WHERE and KEEP

data teens;
   set sashelp.class;
   where age >= 15;
   keep name age height;
run;

proc print data=teens;
run;

Obs    Name       Age    Height

  1    Janet       15     62.5
  2    Mary        15     66.5
  3    Philip      16     72.0
  4    Ronald      15     67.0
  5    William     15     66.5

WHERE filters rows as they're read, so rows that don't match never enter the step — efficient for big data sets. It can only test variables that exist in the input.
KEEP lists the variables to write; DROP lists the ones to leave out. Columns stay in their original order.

The subsetting IF

An IF with no THEN keeps only rows where the condition is true. Unlike WHERE, it can test variables you just calculated:

data heavy;
   set sashelp.class;
   weight_kg = round(weight * 0.4536, 0.1);
   if weight_kg > 55;
   keep name weight_kg;
run;

proc print data=heavy;
run;

Obs    Name      weight_kg

  1    Philip       68.0
  2    Robert       58.1
  3    Ronald       60.3

RENAME and data set options

RENAME old=new; renames a variable in the output. Most statements also exist as data set options in parentheses after a data set name — (keep=...), (drop=...), (rename=(old=new)), (where=(...)), (obs=n):

data small;
   set sashelp.class(keep=name sex age rename=(sex=gender));
run;

Writing several data sets at once

OUTPUT writes the current row to a data set immediately. Name several data sets on the DATA statement and choose where each row goes:

data girls boys;
   set sashelp.class;
   if sex = 'F' then output girls;
   else output boys;
run;

Log (abridged):

NOTE: There were 19 observations read from the data set SASHELP.CLASS.
NOTE: The data set WORK.GIRLS has 9 observations and 5 variables.
NOTE: The data set WORK.BOYS has 10 observations and 5 variables.

Once a step contains an explicit OUTPUT, SAS no longer writes rows automatically at RUN — only your OUTPUT statements do.

Common mistakes

Using WHERE on a calculated variable — SAS stops with an error that the variable is not on the input data set. Use a subsetting IF.
Forgetting that KEEP doesn't reorder columns. To choose the order, use a RETAIN or LENGTH statement listing them before the SET.