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What is the word meaning of subset

A part of a larger group of related things.

Where do we need to subset data in terms of variables

Earlier lessons focused on subsetting observations using `where` or `if` logic
In this lesson, we focus on selecting only the required variables from an existing dataset
Variable subsetting reduces clutter and creates output datasets tailored to the programming task

Create sample input datasets

data class;
   set sashelp.class;
run;
 
data cars;
   set sashelp.cars;
run;

`class` and `cars` will be used in the examples below
Review the datasets and notice that they contain many more variables than may be needed for a particular task

Subset variables using the KEEP statement

The `keep` statement lists the variables that should be written to the output dataset
All other variables are excluded from the final output dataset

Create a dataset named age by keeping the variables Name and Age from class dataset

Notice in the log how many variables are written to the output dataset
Only the listed variables appear in the dataset `age`

data age;
   set class;
   keep name age;
run;

Inspect `age` and confirm that all other variables from `class` are absent
This is one of the most direct ways to subset variables in a DATA step

Create a dataset named height_weight by keeping the variables Name, Height, and Weight from class dataset

This is the same idea as the previous example, but with a different variable list
Only `name`, `height`, and `weight` are stored in the output dataset

data height_weight;
   set class;
   keep name height weight;
run;

Compare `height_weight` with `class` and confirm that only the required variables remain

Subset variables using the KEEP dataset option

The KEEP dataset option performs variable subsetting while the dataset is being read
This can be more efficient because unnecessary variables are not even brought into the DATA step processing area

data age_height;
   set class(keep=name age height);
run;

`age_height` contains only the variables listed in the KEEP dataset option
Compare this approach with the KEEP statement, and note that both achieve a similar final dataset

Subset variables by dropping unwanted variables

Sometimes it is easier to list the variables you do not want rather than the variables you want
In that situation, the `drop` statement or DROP dataset option is useful

data class_drop;
   set class;
   drop sex height weight;
run;

`class_drop` contains all variables from `class` except the variables listed on the DROP statement
This is especially convenient when only a small number of variables need to be removed

Key points to remember

Variable subsetting controls which columns are written to the output dataset
Use `keep` when it is easier to list the variables to retain
Use `drop` when it is easier to list the variables to remove
Dataset options such as `keep=` can subset variables as the dataset is read