DSCI 325: Handout 15 Introduction to SAS Macro Programming Spring 2017

Transcription

1 DSCI 325: Handout 15 Introduction to SAS Macro Programming Spring 2017 The Basics of the SAS Macro Facility Macros are used to make SAS code more flexible and efficient. Essentially, the macro facility is a tool for text substitution. In your program, you associate a macro reference with text (i.e., an actual text string, a variable name, or a numerical value). When the macro processor encounters this reference, it replaces it with the associated text in the SAS program that is built by the macro. The two main components of the SAS macro facility are SAS macro variables With these, you can create references to a variable name, a numerical value, or a text string. The names of macro variables are always prefixed with an ampersand (&). SAS macro programs These use macro variables and macro programming statements to build SAS programs. Macro names are always prefixed with a percent sign (%). Creating a Macro Variable with %LET The easiest way to assign a value to a macro variable is with the %LET statement. The general form of this statement is shown below: %LET macro-variable-name = value; Once a macro variable has been specified, you can refer to this value by using &macro-variable-name within your code. For example, import the FactsonAging.csv file and store it in your personal library in a data set named FactsPre. Then, consider the following code which prints the outcomes and summarizes the responses to a single question from this survey. TITLE 'Question PreQ1'; PROC PRINT DATA=Hooks.FactsPre NOOBS; VAR StudyID PreQ1; ODS NOPROCTITLE; PROC FREQ DATA= Hooks.FactsPre; TABLE PreQ1; 1

2 Portion of the PROC PRINT Output PROC FREQ Output Now, suppose you wanted to re-run this analysis for the second question on the survey. What would you have to change? In this case, it doesn t take much effort on our part to make such minor changes. However, in other examples, you may find yourself having to change a variable name over and over again. To make this process more efficient, we can incorporate the use of a macro variable. %LET Question=PreQ1; TITLE "Question &Question"; PROC PRINT DATA=Hooks.FactsPre NOOBS; VAR StudyID &Question; ODS NOPROCTITLE; PROC FREQ DATA= Hooks.FactsPre; TABLE &Question; Now, to run this program for the second question, we need only change one value: %LET Question=PreQ2; TITLE "Question &Question"; PROC PRINT DATA=Hooks.FactsPre NOOBS; VAR StudyID &Question; ODS NOPROCTITLE; PROC FREQ DATA= Hooks.FactsPre; TABLE &Question; 2

3 Portion of the PROC PRINT Output PROC FREQ Output Comment: Note that the TITLE statement used above contained double quotation marks. What happens if you try to use single quotation marks? %LET Question=PreQ2; TITLE 'Question &Question'; PROC PRINT DATA=Hooks.FactsPre NOOBS; VAR StudyID &Question; 3

4 Writing and Invoking a Macro Program Suppose you wanted to analyze the results of all 25 questions on the pre-test. You could edit the previous code several more times; however, it is much more efficient to write a macro program to accomplish this. Consider the following code. %MACRO SurveyResults; %DO Number = 1 %to 25; %LET Question=PreQ&Number; TITLE "Question &Question"; PROC PRINT DATA=Hooks.FactsPre NOOBS; VAR StudyID &Question; ODS NOPROCTITLE; PROC FREQ DATA=Hooks.FactsPre; TABLE &Question; %MEND SurveyResults; To invoke your macro, use the following statement: %SurveyResults 4

5 Substituting Text with Macro Variables Consider the data in the file CarAccidents.csv. Import this file and save it to your personal library. The code below uses a macro variable to read in only the females over 30. %LET MacGender = Female; %LET MacAge = Over 30; TITLE "&MacGender &MacAge"; PROC PRINT DATA=Hooks.CarAccidents; WHERE Gender = "&MacGender" and Age_Group = "&MacAge"; Note that there are no quotation marks around Female or Over 30 in the above code. Everything except for leading and/or trailing blanks that appears between the equal sign and the colon will become part of the value for the macro variable. A portion of the output is shown below: 5

6 Adding Parameters to Macros Macros become even more flexible when parameters are added. Consider the following example (which does not involve macro parameters). %LET PrintData = Hooks.CarAccidents; %LET Vars = Gender Seat_Belt; %MACRO PrintIt; TITLE "Data Set Name: &PrintData"; VAR &Vars; %MEND Printint; %Printit In the above code, the macro variables named PrintData and Vars have been defined globally; that is, they could also be referenced outside of the macro program. A portion of the result is shown below. Instead of using the %LET statements, we could have defined the macro variables locally inside the macro and then added parameters to our macro as follows: %MACRO PrintIt (PrintData =, Vars = ); TITLE "Data Set Name: &PrintData"; VAR &Vars; %MEND Printint; %Printit (PrintData = Hooks.CarAccidents, Vars = Gender Seat_Belt) These macro variables can now be referenced only within the Printit macro. 6

7 Writing Macros with Conditional Logic Consider the previous macro program, Printit. Suppose you wanted to use this macro to print out a listing of all variables and their values for a given data set with a large number of variables. This macro would not lend itself well to such a task! We can use conditional logic to improve the functionality of our macro program: %MACRO PrintIt (PrintData =, Vars = ); %IF &Vars = all %THEN %DO; TITLE "Data Set Name: &PrintData"; %ELSE %DO; TITLE "Data Set Name: &PrintData"; VAR &Vars; %MEND Printint; %Printit (PrintData = Hooks.CarAccidents, Vars = all) A portion of the output is shown below: 7

8 Displaying System Information SAS comes with some automatic macro variables that you can reference in your programs. A few of these are shown below. Macro Variable Name &SYSDATE &SYSTIME &SYSDAY &SYSVER Description The character value of the date the SAS session began The time the SAS session began The day of the week the SAS session began The version of SAS used For example, consider the following program. %MACRO PrintIt (PrintData =, Vars = ); %IF &Vars = all %THEN %DO; TITLE1 "As of &SYSTIME &SYSDAY &SYSDATE"; TITLE2 "Data Set Name: &PrintData"; %ELSE %DO; TITLE1 "As of &SYSTIME &SYSDAY &SYSDATE"; TITLE2 "Data Set Name: &PrintData"; VAR &Vars; %MEND Printint; %Printit (PrintData = Hooks.CarAccidents, Vars = all) 8

9 SAS System Options Useful for Debugging Macros Some system options that may be helpful when debugging your macros are MPRINT, MLOGIC, and SYMBOLGEN. Each of these options adds some information to your SAS log. Like any other system options in SAS, you can turn them on/off using an OPTIONS statement, as shown below. OPTIONS MPRINT MLOGIC SYMBOLGEN; *OPTIONS NOMPRINT NOMLOGIC NOSYMBOLGEN; %MACRO PrintIt (PrintData =, Vars = ); %IF &Vars = all %THEN %DO; TITLE1 "As of &SYSTIME &SYSDAY &SYSDATE"; TITLE2 "Data Set Name: &PrintData"; %ELSE %DO; TITLE1 "As of &SYSTIME &SYSDAY &SYSDATE"; TITLE2 "Data Set Name: &PrintData"; VAR &Vars; %MEND Printint; %Printit (PrintData = Hooks.CarAccidents, Vars = all) The MPRINT option displays all resolved macro code in the log window. MPRINT(PRINTIT): TITLE1 "As of 09:07 Monday 29FEB16"; MPRINT(PRINTIT): TITLE2 "Data Set Name: Hooks.CarAccidents"; NOTE: Writing HTML Body file: sashtml.htm MPRINT(PRINTIT): PROC PRINT DATA = Hooks.CarAccidents NOOBS; MPRINT(PRINTIT): The MLOGIC option traces the execution of the macro. MLOGIC(PRINTIT): Beginning execution. MLOGIC(PRINTIT): Parameter PRINTDATA has value Hooks.CarAccidents MLOGIC(PRINTIT): Parameter VARS has value all MLOGIC(PRINTIT): %IF condition &Vars = all is TRUE The SYMBOLGEN option displays resolved macro variable names in the log window. SYMBOLGEN: Macro variable VARS resolves to all SYMBOLGEN: Macro variable SYSTIME resolves to 09:07 SYMBOLGEN: Macro variable SYSDAY resolves to Monday SYMBOLGEN: Macro variable SYSDATE resolves to 29FEB16 SYMBOLGEN: Macro variable PRINTDATA resolves to Hooks.CarAccidents SYMBOLGEN: Macro variable PRINTDATA resolves to Hooks.CarAccidents 9

10 Storing Macro Programs Assume your macro programs are stored in a shared folder: /folders/myfolders/sas Programs. Suppose the Printit macro discussed earlier has been saved as a SAS program in this folder. The simplest way to use this macro during a SAS session is to use the %INCLUDE statement. For example, to use this macro to print the CarAccident data, you would need only these two lines of code: %INCLUDE "/folders/myfolders/sas Programs/PrintIt.sas"; %PrintIt (PrintData = Hooks.CarAccidents, Vars = all); 10