SAS Programming Basics

Transcription

1 SAS Programming Basics

2 SAS Programs SAS Programs consist of three major components: Global statements Procedures Data steps

3 SAS Programs Global Statements Procedures Data Step

4 Notes Data steps and procedures are made up of one or more statements. All statements end with a semicolon. This is the only restriction, SAS programs are otherwise freeform e.g. the following are equivalent: proc sort data=mysas.fish out=work.fish2; run; by lt hg; proc sort data=mysas.fish out=work.fish2;by lt hg;run;

5 Notes The run statement is optional (only the final one is required). The run statement indicates to SAS that the procedure or data step is complete. Starting a new data step or procedure is also taken by SAS as an indication that the previous one is complete (nesting of data steps and/or procedures is not allowed). Using the run statement is generally good practice

6 SAS Data Set Basics SAS data set reference Two levels: libref.data-set libref is the SAS library (work library is default if libref is omitted) data-set is the name of the SAS data set SAS naming conventions Names can be up to 32 characters in length Not case sensitive Must begin with a letter or underscore Contain only letters, numbers or underscores Applies to data sets, variables and libraries, but libraries are limited to 8 characters.

7 SAS Data Libraries A SAS data library is a directory on your computer where SAS data sets are stored or will be stored. A library reference name (libref) can be assigned using the libname statement: libname libref path-specification ; The libref must follow naming conventions and the path specified must exist.

8 SAS Data Set Basics SAS data sets consist of two portions Descriptor portion Data portion Descriptor portion Contains various status information Can be viewed with PROC CONTENTS

9 The Contents Procedure To view the descriptor portion of a data set: proc contents data=libref.filename; run; To view data set listing for a particular library: proc contents data=libref._all_ nods; run; Keyword to display all data sets in library Suppress descriptor portion

10 Quick Exercise Assign a library reference to the Orion sub-folder of the SAS Programming Data folder; then run PROC CONTENTS on this library.

11 SAS Data Set Basics Data portion Contains variable names and values Can be viewed with various procedures or via the explorer. SAS variables and values are of two types Numeric Character

12 The Print Procedure The print procedure is primarily used to display raw data. In its most basic form, it simply sends the data to the output window. Print does allow for some levels of customization and summarization.

13 General Syntax proc print data=sas-data-set options ; var variable-list ; by <descending> variable-list ; pageby variable-list ; id variable-list ; sum variable-list ; sumby variable-list ; run; Invoke the procedure with options (including data set)

14 General Syntax proc print data=sas-data-set options ; var variable-list ; by <descending> variable-list ; pageby variable-list ; id variable-list ; sum variable-list ; sumby variable-list ; run; Select the set of variables (columns) to display default is all

15 descending is optional here. In SAS help optional keywords are enclosed in < >; however, they are not actually typed when the option is used General Syntax proc print data=sas-data-set options ; var variable-list ; by <descending> variable-list ; pageby variable-list ; id variable-list ; sum variable-list ; sumby variable-list ; run; Group by a particular variable(s), data set must be sorted.

16 General Syntax proc print data=sas-data-set options ; var variable-list ; by <descending> variable-list ; pageby variable-list ; id variable-list ; sum variable-list ; sumby variable-list ; run; If by variables are used, this statement can be included to get page breaks.

17 General Syntax proc print data=sas-data-set options ; var variable-list ; by <descending> variable-list ; pageby variable-list ; id variable-list ; sum variable-list ; sumby variable-list ; run; Used in conjunction with by to alter the display of groups.

18 General Syntax proc print data=sas-data-set options ; var variable-list ; by <descending> variable-list ; pageby variable-list ; id variable-list ; sum variable-list ; sumby variable-list ; run; Self explanatory only applicable to numeric variables.

19 General Syntax proc print data=sas-data-set options ; var variable-list ; by <descending> variable-list ; pageby variable-list ; id variable-list ; sum variable-list ; sumby variable-list ; run; If by variables are used, this will permit altering sub-totals.

20 Simple Examples Try this: proc print data=mysas.fish; var name elv sa z hg; run; Vs. this: proc print data=mysas.fish label; var name elv sa z hg; run; Vs. this: proc print data=mysas.fish label noobs; var name elv sa z hg; run; Most SAS procedures will use labels whenever present, PRINT does not. The observation column can be removed.

21 Using BY Processing (and SORT) Any time a BY statement is used in a procedure, the data set must be sorted on the listed variables. The sort procedure can be used to sort a data set. Syntax: proc sort data=sas-data-set <out=sas-data-set > ; by <descending > variable1 <descending > variablek; run; Sorts by first variable listed, then by the second variable within each group of the first, and so on.

22 An Example with BY Groups proc sort data=mysas.fish out=work.fish_sort; by lt; run; title 'Grouped by Lake Type'; proc print data=fish_sort label noobs; by lt; var name elv sa z hg; run; Normally the sorted data would replace the previous data set, here an output data set must be specified, why? Remember, as far as SAS is concerned, work.fish_sort and fish_sort are the same data set.

23 Result (First Page)

24 Modification proc print data=fish_sort label noobs; by lt; id lt; var name elv sa z hg; sum hg; run; ID alters the display of by groups. Get totals and sub-totals for hg variable.

25 Result (First Page)

26 Other Statements of Use PRINT is not a very sophisticated procedure, and we will not use it much. But it is good for illustrating some general concepts.

27 Titles and Footnotes General form titlen title text ; footnoten footnote text ; Titles appear at the top of the page, notes at the bottom (default title is The SAS System) n can be any whole number between 1 and 10 (title is equivalent to title1).

28 More on Titles and Footnotes Titles remain in effect for the SAS session unless they are cancelled or changed. Submission of a titlen statement: Replaces previous title with same number Removes all titles with higher number Submission of a null title statement (title;) cancels all titles. Above works same for footnotes.

29 The Label Statement The label statement applies a label to be written in place of the variable name for display label variable1= label1 variable2= label2 ; Labels assigned using the label statement in a procedure are temporary only in effect for that procedure.

30 Example Add the command label name= Name of Lake/Pond'; inside the PROC PRINT to get

31 Output

32 Where Processing One can also subset output using a where statement in any procedure (or data step) where expression; Procedure only processes records for which the expression is true Example: Add the following to your last PRINT. where hg ge 0.5;

33 Relational Operators Relation Symbol Mnemonic Equal = eq Not Equal ^= ne Greater Than > gt Less Than < lt Greater or Equal To >= ge Less or Equal To <= le

34 Compound Conditions Ex. proc print data=fish_sort label noobs; where lt ne. and hg ge 0.5; by lt; id lt; var name elv sa z hg; run;

35 Compound Conditions Ex. proc print data=fish_sort label noobs; where lt ne. and hg ge 0.5; by lt; id lt; var name elv sa z hg; run; The keywords and, or are available along with parentheses to help you set compound conditions.

36 Result

37 Other Operators Between; example: proc print data=fish_sort label noobs; where hg between 0.3 and 0.5; by lt; id lt; var name elv sa z hg; run; In; example: proc print data=fish_sort label noobs; where lt in (1,3); by lt; id lt; var name elv sa z hg; run;

38 General System Options Options statement options SAS-system-options; Option linesize=n pagesize=n date number pageno=n ls=n ps=n nodate nonumber Function Sets the number of characters per line for output. (and log) Sets the number of lines per page for output. (and log) Turns printing of date and time on/off. Turns printing of page numbers on/off. Specifies beginning page number for output.

39 Exercises Create the following output from the fish data set, grouped on both the dam and lt variables (first page shown):

40 Exercises Modify the previous to produce what follows (use a where statement):

41 Exercises Use the projects data set to create:

42 Exercises Since these variables do not have labels, modify the code to include them as follows: