Intermediate SAS: Working with Data

Transcription

1 Intermediate SAS: Working with Data OIT Technical Support Services oit.wvu.edu/training/classmat/sas/ Table of Contents Getting set up for the Intermediate SAS workshop:... 2 Working with Dates... 3 More with Formats and Functions... 4 Working with Data Files... 5 Concatenating data files:... 5 Merging files:... 5 Activity: Merge vs Set... 5 Creating a subset of a data file... 6 Using a procedure to create a new data file... 7 Creating system files... 7 System Options... 8 Error Messages... 9 Common Syntax Errors... 9 Common Data Errors... 9 Reference... 9 Examples of Problem Semicolons: Other Possible Errors: Copyright 2002 West Virginia University

2 Getting set up for the Intermediate SAS workshop: Review of importing an Excel spreadsheet: computers.xls 1. Go to the File menu and select Import Data. 2. Make sure the data source says Excel 97 or 2000 spreadsheet. 3. Click on Next. Then click on the Browse button to find your file. 4. You are looking for computers.xls on your Desktop. When you find the file, click on the Open button to make it appear in the box. Click on Next to continue. 5. Type computer as the member name. Click on Next. 6. Click on Finish. You should be returned to your program editor Enter the following SAS program in your Enhanced Program editor. DATA people; INFILE 'C:\Windows\Desktop\people.txt'; INPUT idno $ bday $ wt paid score gender $; PROC PRINT; RUN; 1. Save this program on your desktop as people.sas. 2. Run the program and review the results. 2 Intermediate SAS

3 Working with Dates 1. Use a date format to read in a date value. Modify your input statement to change the $ after bday to a date informat: INPUT idno bday MMDDYY8.... is a column pointer telling SAS where to start reading the variable. MMDDYY8. is a date format. The 8 tells SAS to allow 8 columns (this gives room for the slashes). Run your program again. What happens? DATE formats DATE7. 05AUG60 DATE9. 05AUG1960 MMDDYY MMDDYY8. 08/05/60 DDMMYY8. 05/08/60 WORDDATE18. August 5, 1960 DOWNAME9. Friday JULIAN NENGO10. S.35/08/05 2. Use a date output format to print out date values. Add a new line after the input statement to reformat bday's date value: FORMAT bday MMDDYY8. ; Run your program again. What happens? Try some of the other DATE formats from the box instead of MMDDYY8. 3. Use the TODAY() function to find out today s date value. Go back to your program and add another line (after FORMAT statement): ANOW = TODAY(); The TODAY function returns today's date as a date/time value (the number of days since 1/1/60). Do not type anything between the parentheses. 4. Compute the person's age Add another line: AGE = (ANOW DATE)/365 ; Run your program again. You should have some new columns of information. DATA people; INFILE 'C:\Windows\Desktop\people.txt'; INPUT idno bday MMDDYY8. wt paid score gender $; FORMAT bday MMDDYY8.; anow=today(); age=(anow-bday)/365; PROC PRINT; RUN; Intermediate SAS 3

4 More with Formats and Functions 1. Use functions to compute square roots, log transformations, maximum, and averages Go back your program and add some new lines to your data step: X = SQRT(SCORE); Y = LOG(SCORE); Z = LOG10(WT); W = MEAN(WT,PAID,SCORE); BIG = MAX(WT,PAID,SCORE); diff = z y; Add a VAR statement after your PROC PRINT; and before your RUN; statement. VAR IDNO X Y Z W BIG; 2. Output formats With the following, don't forget to allow columns for punctuation marks (commas, periods, $, hyphens). Add the following statement to your data step: FORMAT PAID DOLLAR10.2 SCORE ROMAN8. WT 6.2; Add the following procedure to the end and run just that by highlighting it first: proc print; var idno paid score; run; Obs idno paid score $55, XCIV $45, LXXXVIII DATA people; age=(anow-bday)/365; x = SQRT(score); y = LOG(score); z = LOG10(paid); w = MEAN(wt,paid,score); big = MAX(wt,paid,score); diff=z-y; PROC PRINT; VAR idno x y z w big; RUN; 3. Using a format to create categories for frequency tables At the top of your program, add: PROC FORMAT; VALUE grade LOW-59='F' 60-69='D' 70-79='C' 80-89='B' 90-HIGH='A'; VALUE grp LOW-35000='Low' HIGH='High'; At the end of your program, add: PROC FREQ; TABLES score*paid; FORMAT SCORE grade. PAID grp.; RUN; 4 Intermediate SAS

5 Working with Data Files Concatenating data files: Files usually have the same variables and different observations. DATA BOTH; SET one two; DATA BOTH; SET one two; BY IDNO; * will interleave based on id number; * files one & two were sorted by id in a previous step; Merging files: files usually have the same experimental units and different variables DATA COMBINE; MERGE one two; * one-to-one matching; DATA COMBINE; MERGE one two; BY idno; * will use id variable to match observations together; * datasets must be in same sorted order; Activity: Merge vs Set Go to the Enhanced Program Editor Clear your editor: Edit > Clear All Open combine.sas (from the desktop) and run it. Data ONE; input ID YEAR AMT; cards; PROC SORT; BY ID; Data TWO; input ID YEAR AMT; cards; PROC SORT; BY ID; DATA BOTH; SET ONE TWO; PROC PRINT; TITLE 'SET'; DATA BOTH; SET ONE TWO; by ID; PROC PRINT; TITLE 'SET BY'; DATA BOTH; MERGE ONE TWO; PROC PRINT; TITLE 'MERGE'; DATA BOTH; MERGE ONE TWO; by ID; PROC PRINT; TITLE 'MERGE BY'; RUN; Draw a line from each Data step to the correct output. When you are done, clear the contents of all windows. Intermediate SAS 5

6 Creating a subset of a data file Selecting Observations DATA MALES; SET people; IF gender='m'; *subsetting IF; or DATA MALES; SET people; IF gender='f' THEN DELETE; Create 2 data files in one data step: DATA MALES FEMALES; SET people; *set allows you to re-process an existing data set; IF gender='m' then OUTPUT MALES; ELSE IF gender='f' then OUTPUT FEMALES; Selecting Variables DATA new; SET people; DROP score; or DATA another; SET people; KEEP IDNO AGE PAID; Summary of new statements: DELETE: throw out observation DROP: throw out variable(s) IF : (subsetting if): keep observation if condition is true KEEP: retain only these variables OUTPUT: write an observation out to a data set 6 Intermediate SAS

7 Using a procedure to create a new data file PROC MEANS NOPRINT data=people; BY date; VAR paid score; OUTPUT OUT=newfile MEAN=avgpd avgscor N=n1 n2; PROC PRINT data=newfile; VAR date avgpd avgscor n1 n2; RUN; New option for proc means statement: NOPRINT: don't do typical means results New statement: OUTPUT OUTPUT OUT=filename statistic=new_varname(s); PROC REG data=people; MODEL score=wt; OUTPUT OUT=new2 P=predscor R=resid; PROC PLOT data=new2; PLOT predscor*score; PLOT resid*idno; RUN; QUIT; P creates variable for predicted values; R for residuals (actual predicted) Creating system files LIBNAME more 'C:\Windows\Desktop\'; DATA more.stuff; SET people; This will create a file named: stuff.sas7bdat in the folder you specified. To use existing system files in new programs: 1. First include the appropriate LIBNAME statement 2. Then specify the library and member name: PROC xxx DATA=lib.member; DATA new; SET lib.member; IF var=value; PROC FREQ DATA=more.stuff; DATA subset; SET more.stuff; IF gender='f'; Intermediate SAS 7

8 System Options The OPTIONS statement can appear anywhere in a SAS program and can appear more than once. OPTIONS set stay in effect until they are reset later in the program. NONOTES suppress notes and warning messages in SAS LOG NODATE suppress date on OUTPUT NONUMBER suppress page number on OUTPUT NOCENTER left justify the OUTPUT PS: PageSize how many lines per page (OUTPUT) LS: LineSize how many characters per line (OUTPUT) Default values for SAS/Windows: OPTIONS NOTES DATE NUMBER CENTER PS=67 LS=84; OPTIONS NODATE NOCENTER PS=84 LS=72; To switch back to the defaults, delete the no prefix: OPTIONS NOTES DATE NUMBER CENTER; FIRSTOBS which observation to start on OBS number of observations to read in To read only a portion of a huge data file (lines 100 through 500, inclusive): OPTIONS FIRSTOBS=100 OBS=500; To see what the setting is for a particular option: proc options option=linesize; run; General Tips Make backup copies of programs and data on multiple media. Keep records of what you do to your data and your programs Write comments in your program to document what you are doing: /* comment */ Use /* */ comments to block out statements you do not wish to run at this time When possible, keep data in a separate file and use an infile statement Use formats and labels to make output easier to read If variable names are like: q1, q2, q3... Q10, you can refer to them as q1-q10 You can specify a list of variables from input statement: bday -- gender; You can factor table requests in proc freq: tables age*(paid wt score); 8 Intermediate SAS

9 Error Messages Common Syntax Errors leaving out ; putting ; in instream data misspelling/mistyping variable name or option invalid variable name forgetting closing quote mark forgetting END; statement (needed when using DO) Common Data Errors using wrong input format specifying wrong columns O vs 0 (oh vs zero) extra blank line not using. for missing data in free-format list format using.. (multiple periods) for missing data Reference SAS Guide to Problem Solving and Error Messages (Version 5 Edition), ISBN Intermediate SAS 9

10 Examples of Problem Semicolons: data; input x y z cards; proc print; ERROR : Statement is not valid or it is used out of proper order. ERROR: No CARDS or INFILE statement. 7 data 18 input x y z; 19 cards; NOTE: The data set WORK.INPUT has 1 observations and 0 variables. NOTE: The data set WORK.X has 1 observations and 0 variables. NOTE: The data set WORK.Y has 1 observations and 0 variables. NOTE: The data set WORK.Z has 1 observations and 0 variables. 23 proc print; NOTE: No variables in data set WORK.Z. 26 data ; 27 input x y z; 28 cards; NOTE: The data set WORK.DATA3 has 2 observations and 3 variables. NOTE: The DATA statement used 0.88 seconds ; ERROR : Statement is not valid or it is used out of proper order. Other Possible Errors: 44 data ; 45 input x y z; 46 q=sqrt(x); NOTE: Invalid argument to function SQRT at line 46 column 3. X=-1 Y=2 Z=3 Q=. _ERROR_=1 _N_=1 Mathematical operations could not be performed at the following places. The results of the operations have been set to missing values. NOTE: Missing values were generated as a result of performing an operation on missing NOTE: SAS went to a new line when INPUT statement reached past the end of a line. NOTE: LOST CARD. 10 Intermediate SAS