SAS programming (600 USD)

Mentor: Anirban Dhar  Contact: ani_bit@hotmail.com / 978 996 0551

INTRODUCTION TO SAS 1. What is SAS system? 2. The SAS language 3. SAS data sets 4. SAS Variables 5. The two parts of a SAS program 6. The DATA step’s built-in loop 7. The SAS Log and Output files 8. Using SAS system for Windows 9. Using SAS system options 10. HELP!!!

Mentor: Anirban Dhar  Contact: ani_bit@hotmail.com / 978 996 0551

INTRODUCTION TO SAS 1. What is SAS system? SAS system is an integrated applications system that provides complete data processing and analysis capabilities. • SAS can access variety types of data. • Data management features include updating, rearranging, combining, editing, and subsetting (and many more). • Analytical tools range from simple descriptive statistics to more advanced and specialized analyses for biostatistics and epidemiologic applications (and many others). • Data presentation capabilities range from simple lists and tables to multidimensional plots and full-color graphics. 2. The SAS language SAS provides a full-featured, high-level programming language that gives you total control over your data. SAS programs • A SAS program is a sequence of statements: Executable and nonexecutable statements. • SAS statements are step-by-step instructions that tell SAS to perform specific tasks. • Each group of statements is called a SAS step: Data step and Proc step. • SAS programs may consist of one or many SAS steps. SAS statements • Every SAS statement ends with a semicolon (;). • SAS statements can be in upper or lower case, can take up more than one line, and can start in any column. Errors • Syntax errors are errors made in SAS statements. Examples are misspelled keywords, missing semicolons, unmatched quotes, and other punctuation errors. • Data errors occur when data values do not match the values expected. An example is not specifying a character variable ($) for character data in the INPUT statement. • Logic errors occur when conditions and/or sequence of SAS statement are written incorrectly. SAS does not produce error messages for logic errors, so the errors could only be found in unexpected results. Examples are mis-specified conditions and misplaced SAS statements. 3. SAS data sets SAS reads data and organizes the data into a SAS data set. • Data must be stored in a SAS data set for SAS to be able to identify and access. • SAS can then be used to display, revise, and analyze data. SAS data sets contain data values organized into variables and observations. • A variable is a set of data values that describe a specific characteristic (e.g. age or gender). • Each column of data values in a SAS data set is a variable. • Each variable is identified by a variable name. • An observation is a set of data values for the same item (e.g., person or visit). • Each row of data values in a SAS data set is an observation. 4. SAS Variables • In SAS Version 8, variable names may be up to 32 characters long (8 characters in Version 6), start with a letter or _ (underscore), and cannot include special characters (%, &, $, #, @, *, !). • Numeric data may contain numbers, +,-, decimal points, scientific notation (E). • Character data may contain anything. • Missing numeric data are represented by a dot (.); missing character data are represented by a blank (‘ ’). 5. The two parts of a SAS program The DATA step • A SAS Data step is a group of statements that builds a SAS data set. • Each Data step begins with a DATA statement and ends with a RUN, DATA or PROC statement. • The purpose of a Data step is to create or modify data. Data steps may also be used to produce raw data (ASCII file) from an existing SAS data set. • Data steps generally produce no results or reports in the SAS Output window. The PROC step • A SAS Proc step (or a SAS procedure) is a prewritten computer program that processes or analyzes SAS data sets. • Each Proc step begins with a PROC statement and ends with a RUN, DATA or PROC statement. • The purpose of a Proc step is to perform a specific analysis or function. • Proc steps generally produce results or reports in the SAS Output window. 6. The DATA step’s built-in loop DATA steps execute line-by-line and observation-by-observation. • SAS reads the DATA statement, creates the structure of a SAS data set, and marks the statement as the point to begin processing for each data line. • SAS assigns missing values to all variables (except the special variable _N_) before the INPUT statement is executed. _N_ is incremented by one for each iteration of the data step (_N_=1 before the first iteration; _N_=2 before the second iteration). • SAS uses the description in the INPUT statement to read the data line and produce an observation, substituting the actual data values for the missing values. These values are placed in the Program Data Vector (PDV), which is a temporary holding area where data values are held before being written to the SAS data set. • SAS then uses the observation to execute any other SAS statements that are present (creation of new variables, variable recodes, etc.). • Finally, SAS adds the observation to the data set being created. • This cycle continues until all the observations have been written to the SAS data set. 7. The SAS Log and Output files • The SAS log contains the SAS version number, program statements, number of observations, variables in data set, computer resources used, page numbers to locate output (if any), error messages, warnings, and other notes. • Read the log!! • The output file contains any output requested in the SAS program–there may be no output if the program did not request any output. • There may be no output if the program bombed–read the log!! 8. Using SAS system for Windows Writing and editing SAS programs in program editor • Type text of program in editor window, or open existing program by following file-open menu path. • Submit SAS programs or to edit other text files (e.g., data and output files). • Graphical environment enables use of edit menu for cutting and pasting, etc. Executing programs • Use locals-submit menu path to submit program. Viewing the log and output • Click on the appropriate window or choose globals-log (for SAS log) or globals-output (for program output) menu path. • Use help-keys to see how function keys are defined. • Use edit-clear text to clear window. • Use locals-recall text to get program back in editor window. 9. Using SAS system options • System options stay in effect for duration of SAS session. • To see current system settings, type: PROC OPTIONS; RUN; • OPTIONS statement: keyword options followed by the option. • Common options include: center | nocenter, date | nodate, number | nonumber, linesize=n where n=64-256, pagesize=n where n=15-32767, pageno=x (x=1 if you want page no.1 to be at the top of each new requested output during a SAS session), compress=yes. 10. HELP!!! • www.sas.com SAS online documentation