SAS Data Step

Data Model

The data model for SAS is:

• Read a row of data
• Process statements sequentially

• On run, write data into the output table

data LIBREF.TABLE;
  STATEMENTS;
run;

Tables

The table named in a data step is always the output table. By default it is also the input table and data is manipulated in place.

To set a different table as the input, use a set statement.

data LIBREF.OUTPUT;
  set LIBREF.INPUT;
  STATEMENTS;
run;

Transforming Data

Creating Variables

data LIBREF.OUTPUT;
  set LIBREF.INPUT;

  /* declare numeric variables directly with numeric literals */
  foo = 1;

  /* declare string variables by specifying the length first, then with string literals */
  length hello $5 world $5;
  hello = 'Hello';
  world = 'World';

  /* the length of a string variable cannot be changed again within the same data step */
  length greeting $12;
  greeting = CAT(hello, world);        /* 'Hello World'  */
  greeting = CATS(hello, world);       /* 'HelloWorld'   */
  greeting = CATX(', ', hello, world); /* 'Hello, World' */
  greeting = hello||world;             /* 'HelloWorld'   */
run;

Any valid expression can be used to create a new variable.

Coercing Data Types

data LIBREF.NEWTABLE;
  set LIBREF.OLDTABLE;

  /* coerce string to numeric */
  numeric_zip_code = input(string_zip_code, 5.);

  /* left-align text */
  length TEXT_VAR $999.;
  TEXT_VAR = put(TEXT_VAR, $999. -L);

  /* parse timestamps like '01Jan1999' */
  format timestamp DATE9.;
  month = month(timestamp);

  /* round numerics to integers */
  format test_score 3.;
run;

The input function generates a variable _ERROR_ by default, flagging cases that could not be formatted. To suppress this variable's creation, use input(ALNUM_ID, ?? 8.).

Filtering Data

Subset Cases

To subset the cases of a data table, use where statements.

data LIBREF.NEWTABLE;
    set LIBREF.OLDTABLE;
    where EXPR;
run;

Alternatively, toggle the output data table with if statements.

data LIBREF.NEWTABLE1;
    set LIBREF.OLDTABLE;
    if EXPR then output LIBREF.NEWTABLE1; else output LIBREF.NEWTABLE2;
run;

Subset Variables

To subset the variables of a data table, use keep and drop statements.

data LIBREF.NEWTABLE;
    set LIBREF.OLDTABLE;
    keep VARLIST1;
    drop VARLIST2;
run;

De-duplication

This is actually best done using the SORT procedure. See here for details.

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