Macro Programming Essentials for Data Analysis

1. FOR MONDAY: • Be prepared to hand in a one-page summary of the data you are going to use for your project and your questions to be addressed in the project • Read Chapter 7 (7.1-7.5) on Macro-Programming: • macros allow you to make small changes in code that ripple throughout a long program • macros allow you to write a piece of code once and reuse it many times over… • macros allow you to make you code data dependent - SAS decides what to do based on the values of the data. • Practice macro writing on the project data…

2. Macros and macro variables • The macro processor “resolves” your macro code so it can generate legitimate SAS code. • SAS macro code consists of macros and macro variables. Macro variables are prefaced with an ampersand (&) and macros are prefaced with a percent sign (%). A macro can be a complex piece of code with DATA steps, PROC steps and macro statements like %DO or %LET, etc. A macro variable has only one value, always a character.

3. Macro variables • Create a macro variable by using the %LET statement. This is an efficient way to replace text strings in SAS... %LET macro-variable-name = text-value ; • Then to use that particular text string in a SAS program refer to the macro variable with an ampersand (&). Note quotes not required around the “text-value”. e.g., %LET X = freshman; title “Data analysis for the &X Class”;

4. NOTE the difference between a global and a local macro variable: %LET outside a macro definition defines a global variable. Otherwise, the macro variable is local. • Try the example program on page 203 - note that the code only has to be changed in one place in the program.

5. Macro definitions • Macros allow you to substitute text of SAS code within a SAS program. • Each macro has a name and is defined between the %MACRO and the %MEND statements... E.g., %MACRO macro-name; macro-definition %MEND macro-name; • To invoke the macro definition you defined as above, use the statement %macro-namewithin your SAS program and the text in the macro-definition will be executed...

6. See the example in Section 7.3 on p. 205. • or this example… %macro plot; proc plot; plot totmass*plantht; run; %mend plot; Later you may use this macro as: data temp; set save.padgett; if marsh=“ph” ; run; %plot proc print; run; etc.....

7. The above macros would be much more useful if we could pick the variables we want to plot... this requires the use of parameters within the macro. • E.g.: %macro plot(yvar= ,xvar= ); proc plot; plot &yvar*&xvar; run; %mend plot; Then invoke the macro by referring to it and also inserting the specific variables you want to plot: %plot(yvar=totmass, xvar=plantht) • Do the example on page 207 - the macro %SELECT is created with 2 parameters creating 2 macro variables &CUSTOMER and &SORTVAR.

8. Use the data (custID, sale date, variety sold, quantity) 240W 02-07-2003 Ginger 120 240W 02-07-2003 Protea 180 356W 02-08-2003 Heliconia 60 356W 02-08-2003 Anthurium 300 188R 02-11-2003 Ginger 24 188R 02-11-2003 Anthurium 24 240W 02-12-2003 Heliconia 48 240W 02-12-2003 Protea 48 356W 02-12-2003 Ginger 240

9. We may use conditional logic in macros to write different code depending upon the value of certain macro variables for example: %MACRO dailyreports; %IF &SYSDAY = Monday %THEN %DO; PROC PRINT DATA = flowersales; FORMAT SaleDate WORDDATE18.; TITLE 'Monday Report: Current Flower Sales'; %END; %ELSE %IF &SYSDAY = Tuesday %THEN %DO; PROC MEANS DATA = flowersales MEAN MIN MAX; CLASS Variety; VAR Quantity; TITLE 'Tuesday Report: Summary of Flower Sales'; %END; %MEND dailyreports; DATA flowersales; INFILE 'c:\MyRawData\TropicalSales.dat'; INPUT CustomerID $ @6 SaleDate MMDDYY10. @17 Variety $9. Quantity; RUN; %dailyreports RUN;

10. Note that SAS creates automatic macro variables that you may use in your programs: &SYSDATE is the character value of the date that the session began &SYSDAY is the character value of the day of the week that the session began… end chapter 7… next time we’ll do graphics…