1. Introduction
This module illustrates how to create and use labels in SAS. There are two main items that can be labeled, variables and values. Once created these labels will appear in the output of statistical procedures and reports that you may produce from SAS. They are also displayed by some of the SAS/GRAPH procedures.
The program below reads the data and creates a temporary data file called auto. The labeling shown in this module are all applied to this data file called auto.
DATA auto ; INPUT make $ mpg rep78 weight foreign ; CARDS; AMC 22 3 2930 0 AMC 17 3 3350 0 AMC 22 . 2640 0 Audi 17 5 2830 1 Audi 23 3 2070 1 BMW 25 4 2650 1 Buick 20 3 3250 0 Buick 15 4 4080 0 Buick 18 3 3670 0 Buick 26 . 2230 0 Buick 20 3 3280 0 Buick 16 3 3880 0 Buick 19 3 3400 0 Cad. 14 3 4330 0 Cad. 14 2 3900 0 Cad. 21 3 4290 0 Chev. 29 3 2110 0 Chev. 16 4 3690 0 Chev. 22 3 3180 0 Chev. 22 2 3220 0 Chev. 24 2 2750 0 Chev. 19 3 3430 0 Datsun 23 4 2370 1 Datsun 35 5 2020 1 Datsun 24 4 2280 1 Datsun 21 4 2750 1 ; RUN; PROC CONTENTS DATA=auto; RUN;
The output of the proc contents is shown below. You can see in this portion of the output of the proc contents that there are no labels attached to the variables in this file.
-----Alphabetic List of Variables and Attributes----- # Variable Type Len Pos ----------------------------------- 5 FOREIGN Num 8 32 1 MAKE Char 8 0 2 MPG Num 8 8 3 REP78 Num 8 16 4 WEIGHT Num 8 24
2. Creating variable labels
We use the label statement in the data step to assign labels to the variables. You could also assign labels to variables in proc steps, but then the labels only exist for that step. When labels are assigned in the data step they are available for all procedures that use that data set.
The following program assigns variable labels to rep78, mpg and foreign.
DATA auto2;
SET auto;
LABEL rep78 ="1978 Repair Record"
mpg ="Miles Per Gallon"
foreign="Where Car Was Made";
RUN;
PROC CONTENTS DATA=auto2;
RUN;
Looking at the output produced by the proc contents step shows that the labels were indeed assigned. The relevant part of this output follows.
-----Alphabetic List of Variables and Attributes----- # Variable Type Len Pos Label --------------------------------------------------------- 5 FOREIGN Num 8 32 Where Car Was Made 1 MAKE Char 8 0 2 MPG Num 8 8 Miles Per Gallon 3 REP78 Num 8 16 1978 Repair Record 4 WEIGHT Num 8 24
These labels will also appear on the output of other procedures giving a fuller description of the variables involved. This is demonstrated in the proc means below.
PROC MEANS DATA=auto2; RUN;
Looking at the output produced by the proc means shows that the labels were indeed assigned. Look at the column titled Label. The relevant part of this output follows.
Variable Label N Mean Std Dev Minimum -------------------------------------------------------------- MPG Miles Per Gallon 26 20.9230769 4.7575042 14 REP78 1978 Repair Record 24 3.2916667 0.8064504 2 WEIGHT 26 3099.23 695.0794089 2020 FOREIGN Where Car Was Made 26 0.2692308 0.4523443 0 -------------------------------------------------------------
3. Creating and using value labels
Labeling values is a two step process. First, you must create the label formats with proc format using a value statement. Next, you attach the label format to the variable with a format statement. This format statement can be used in either proc or data steps. An example of the proc format step for creating the value formats, forgnf and $makef follows.
PROC FORMAT;
VALUE forgnf 0="domestic"
1="foreign" ;
VALUE $makef "AMC" ="American Motors"
"Buick" ="Buick (GM)"
"Cad." ="Cadillac (GM)"
"Chev." ="Chevrolet (GM)"
"Datsun" ="Datsun (Nissan)";
RUN;
You may include any number of value statements to create label formats as needed. Since make is a variable that contains character values, when you define the formats for it you have to precede the format name with a $ so the format name becomes $makef. Additionally, for character variables the values of the variables must be enclosed in quotes.
Now that the formats forgnf and $makef have been created, they must be linked to the variables, foreign and make. This is accomplished by including a format statement in either a proc or a data step. In the program below the format statement is used in a proc freq.
PROC FREQ DATA=auto2;
FORMAT foreign forgnf.
make $makef.;
TABLES foreign make;
RUN;
Notice that the formats forgnf. and $makef. are each followed by a period in the format statement. This is the way that SAS tells the difference between the name of a format and the name of a variable in a format statement.
The output of the frequencies procedure for foreign displays the newly defined labels instead of the values of the variable.
Where Car Was Made
Cumulative Cumulative
FOREIGN Frequency Percent Frequency Percent
------------------------------------------------------
domestic 19 73.1 19 73.1
foreign 7 26.9 26 100.0
The output of the frequencies procedure for make displays the newly defined labels instead of the values of the variable. Values for which formats haven’t been defined (Audi and BMW) appear in the table without modification.
MAKE Frequency Percent Frequency Percent ------------------------------------------------------------- American Motors 3 11.5 3 11.5 Audi 2 7.7 5 19.2 BMW 1 3.8 6 23.1 Buick (GM) 7 26.9 13 50.0 Cadillac (GM) 3 11.5 16 61.5 Chevrolet (GM) 6 23.1 22 84.6 Datsun (Nissan) 4 15.4 26 100.0
If you link formats to variables in a data step where a permanent file is created, then every time you use that file SAS expects to find the formats. Thus you will have to supply the proc format code in each program that uses the file. Since this can make each of your programs much longer than you might like, I would like to provide a tip for accomplishing this task without repeating the code for the proc format in every program. Assuming that a small program containing only the proc format is stored in a file called fmats.sas in a directory on your C: drive called myfiles, the following statement will bring that code into your current program:
%INCLUDE ‘C:myfilesfmats.sas’;
This should save time and make maintenance of your programs easier. The remainder of your program would follow this statement.
4. Problems to look out for
- Common errors in dealing with value labels are; 1) leaving off the period at the end of the format in a format statement, and 2) leaving off the dollar sign before a character format.
- If you leave out the proc format code in a program using a permanent file where formats are defined SAS will require the formats be available for use. In this case you can either follow the instructions for including code (%include) above, or copy the proc format code into your current program. You can also include the nofmterr option to allow the program to run with out errors.
- Another common error is to reference the format with a format statement before defining the format with proc format code. Simply move your proc format code to the beginning of the program to fix this problem.
5. For more information
- For information on reading data into SAS, see the SAS Learning Module Inputting raw data into SAS.
- For more information about proc freq see the SAS Learning Module Descriptive information & statistics in SAS.
- For more information about options see the SAS Learning Module Common SAS Options.