How to Add Row Numbers in SAS

Row Numbers

Sometimes you need a column in your data set that indicates the row number. This might be useful as an artificial identifier, a rank, or something else. In this article, we explain two ways how to add row numbers in SAS.

Adding Row Numbers with _N_ in a Data Step

The first option to create a column with row numbers is using the automatic _N_ variable. SAS processes input data row by row and the automatic _N_variable stores the current row number. This variable is particularly useful for processing the first or last row. However, since _N_ is a variable you can also use it to add a column with row numbers.

Adding Row Number with monotonic() in PROC SQL

The automatic _N_ variable can only be used in data steps. However, you can use the monotonic() function in PROC SQL. The monotonic function is undocumented and generates sequential numbers.

Example: Adding Row Numbers

In the following example code, we demonstrate how to apply both options of how to add row numbers. First, we create a data set and then we add the row numbers. The three images at the end show the original data set and the two data set with the new column.

/* CREATE A DATA SET */
data work.examscores;
	input name $ score;
	datalines;
Jim 80
Maria 85
Bob 50
Cris 70
John 95
Kate 95
George 80
Susan 75
Joe 55
Jennifer 75
Lu 60
Antonio 85
;
run;

/* ADD ROW NUMBER (I) */
data work.examscores_I;
	set work.examscores;
	
	rownumber_I = _N_;
run;


/* ADD ROW NUMBER (II) */
proc sql;
	create table work.examscores_II as
		select *,
			monotonic() as rownumber_II
		from work.examscores;
quit;

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