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INTRODUCTION TO SAS

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SAS PROGRAMMING

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INTRODUCTION TO SAS

  1. 1. Introduction to SAS BIO 226 – Spring 2011
  2. 2. 2 Outline • Windows and common rules • Getting the data – The PRINT and CONTENTS Procedures • Basic SAS procedures – The SORT Procedure – The MEANS Procedure – The UNIVARIATE Procedure – The FREQ Procedure – The CORR Procedure – The PLOT Procedure • Manipulating the data, e.g., creating new variables • Libraries • Output in Word document • References • Practice Slides 3-7 Slides 8-10 Slide 9 Slide 13 Slides 14-15 Slide 15 Slide 16 Slide 16 Slide 17 Slide 11-12 Slide 18 Slide 19 Slide 20 Slides 21-22
  3. 3. 3 The different SAS windows • Explorer: contains SAS files and libraries • Editor: where you can open or type SAS programs • Log: stores details about your SAS session (code run, dataset created, errors...) • Results: table of contents for output of programs • Output: printed results of SAS programs
  4. 4. 4 Basic SAS rules (1) • Variable names must: – be one to 32 characters in length – begin with letter (A-Z) or underscore (_) – continue with any combination of number, letters or underscores • A variable’s type is either character or numeric • Missing values: – missing character data is left blank – missing numeric data is denoted by a period (.)
  5. 5. 5 Basic SAS rules (2) • Two ways to make comments: – * write comment here; – /* write comment here */ • SAS is insensitive to case
  6. 6. 6 Basic programming rules (1) • SAS programs are composed of statements: these are organized in DATA steps and PROC steps – DATA step: gives dataset a name, manipulates dataset – PROC step: procedure or analysis you want SAS to carry out • SAS reads code line by line and the end of a line is marked by a semicolon. • All SAS programs end with RUN; • Quotes can be single or double.
  7. 7. 7 Basic programming rules (2) • SAS statements are free-format: – Can begin and end in any column – One statement can continue over several lines – Several statements can be on one line • To submit program, highlight the code to run and click on the submit button (running silhouette)
  8. 8. 8 Loading data • If you have SAS data set (sasintro.sas7bdat) you can double click on it and it will load itself. • If you don’t have SAS data set (sasintro.txt), and the first row of your dataset contains the variable names, you can import it using File > Import Data… and specify the directory. • Or you can use the following code: DATA mydata; INFILE ‘g:sharedbio226sasintro.txt’; INPUT weight bmi id age activity education smoking; RUN; • Setting your current directory: on the bottom line of the main SAS window, you should see it set to C:WINDOWSsystem32. Double click on it to change it.
  9. 9. 9 How to view the loaded data? • Go in the Explorer window, double click on Libraries, then Work and sasintro.sas7bdat • To view general information about the data set, like variables’ name and type: PROC CONTENTS DATA=mydata; RUN; • Use the PRINT procedure to view the first 25 records: PROC PRINT DATA=mydata (OBS=25); RUN;
  10. 10. 10 Variables from sasintro.txt # Variable Type Unit 5 activity Num kcal/week 4 age Num years 2 bmi Num kg/m2 6 education Num years 3 id Num 7 smoking Num 1:current smoker, 0:non-smoker 1 weight Num lbs
  11. 11. 11 Manipulating data (1) • selecting a subset of rows DATA mydata_s; SET mydata; IF smoking=1; RUN; • deleting a column (or columns) DATA mydata2; SET mydata; DROP weight education; RUN;
  12. 12. 12 Manipulating data (2) • adding a column (or columns) DATA mydata3; SET mydata; weight_kg=weight*0.453; IF age <= 60 THEN agegroup=1; ELSE IF age<=70 THEN agegroup=2; ELSE agegroup=3; /*drop age;*/ RUN;
  13. 13. 13 Sorting data PROC SORT DATA=mydata OUT=mydata4; BY ID age weight; PROC PRINT DATA=mydata (OBS=5); PROC PRINT DATA=mydata4 (OBS=5); RUN;
  14. 14. 14 Summarizing data (1) • Summarizing weight: PROC MEANS DATA=mydata; VAR weight; RUN; • Summarizing weight in the youngest agegroup: PROC MEANS DATA=mydata3; VAR weight; WHERE agegroup=1; RUN;
  15. 15. 15 Summarizing data (2) • Summarizing weight by smoking status (two possible codes): PROC SORT DATA=mydata OUT=mydata5; BY smoking; PROC MEANS DATA=mydata5; VAR weight; BY smoking; RUN; PROC MEANS DATA=mydata; CLASS smoking; VAR weight; RUN; • All these summarizing measures can be obtained with PROC UNIVARIATE also.
  16. 16. 16 Categorical data and correlation • Summarizing categorical data PROC FREQ DATA=mydata3; TABLES smoking*agegroup /chisq exact; RUN; • Examining correlation PROC CORR DATA=mydata; VAR weight; WITH bmi age; RUN;
  17. 17. 17 Basic procedures: plots • Barcharts PROC CHART DATA=mydata3; VBAR agegroup /DISCRETE; RUN; • Scatterplot PROC PLOT DATA=mydata3; PLOT bmi*weight='*'; RUN; • Histogram, Boxplot, Normal Probability Plot PROC UNIVARIATE DATA=mydata3 PLOT; VAR weight; RUN;
  18. 18. 18 /* Libraries */ • A library is the directory where your SAS dataset is stored. • The default library is named Work and stores your SAS datasets temporarily: they will be deleted when you end your SAS session • If you want to save your SAS datasets and use them again later, create your own library: LIBNAME SAS_Lab 'p:BIO226SAS'; DATA SAS_Lab.mydata; INFILE ‘g:sharedbio226sasintro.txt’; INPUT weight bmi id age activity education smoking; RUN;
  19. 19. 19 SAS output and Word • To send you SAS output to a Word document: ODS RTF FILE=‘p:output.RTF’ style=minimal; PROC CORR DATA =mydata; VAR weight; WITH bmi age; RUN; ODS RTF CLOSE; • Other styles: Journal, Analysis, Statistical
  20. 20. 20 For further references • SAS9 Documentation on the Web: http://support.sas.com/onlinedoc/913/docMainpage.jsp • Applied Statistics and the SAS Programming Language (5th Edition) Ron P. Cody and Jeffrey K. Smith • The Little SAS Book, L.D. Delwiche and S.J. Slaughter • See SAS_help.doc on course website
  21. 21. 21 Try your own • Find the summary statistics (mean, mode, standard deviation,…) for education with PROC UNIVARIATE, as well as a histogram for years of education. • Create a new variable educ_group which breaks years of education into four groups (0-10, 10-15,15-18,18-25). Put this new variable in a new data set and drop the education variable, as well as weight, bmi and age. • Find the number of smokers per education group. • Find the mean physical activity in each education group.
  22. 22. 22 Data name Description mydata original imported data mydata_s only smokers mydata2 dropped weight, education mydata3 added weight_kg, agegroup, dropped age mydata4 sorted original data by age and weight mydata5 sorted original data by smoking status Recap of different datasets created

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