The Basics of PROC FCMP. Dachao Liu Northwestern Universtiy Chicago

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1 The Basics of PROC FCMP Dachao Liu Northwestern Universtiy Chicago ABSTRACT SAS Functions can save SAS users time and effort in programming. Each release of SAS has new functions added. Up to the latest version of SAS 9.3, there are over 450 functions. Even with a vast plethora of SAS functions, some SAS users still find the lack of some functions to perform certain tasks. Fortunately, In SAS 9, a new procedure called PROC FCMP was developed to help SAS users to write their own functions. This paper will discuss the basics of PROC FCMP and how we can use it to build our own SAS functions. The intended audience would be those who have a basic idea of SAS functions. INTRODUCTION Like many other programming languages, SAS has a vast number of built-in functions. A SAS function is a method to perform a task like computation or data manipulation and return a value based on the arguments given. SAS is very rich in built-in functions, saving SAS users tons of time and programming effort. In SAS version 6, there were only 236 functions, In SAS 9, there are almost twice as many. But oftentimes, we still find there is not enough. How can we do this special computation? How can we remove that extra character? How can we use MS Excel functions in SAS? The questions can go on and on. To meet SAS users needs, SAS institute developed a new procedure, PROC FCMP. By using PROC FCMP, we can find answers to those questions. In this paper, I will discuss what is PROC FCMP, and then some examples. DISCUSSION What is a function? In our daily life, by saying something is functioning, we mean something is doing task by rule. The heart is functioning when it plumps blood through the body. In academic field, we also use function to mean performing some tasks by rule, thus creating lots of functions in math and computer languages. They are like machines because they need an input to create an output. So the output is related somehow to the input. Y=9*x is a function. If the input is 8 for x, then the output is 72 for y, and we may write f(8) = 72. The input variable(s) are sometimes referred to as the argument(s) of the function. Like a math function, a SAS function also needs an input in order to create an output. A SAS function is a method to perform a task like computation or data manipulation and return a value based on the arguments given. SAS functions are often categorized by the type of data to be processed and type of task a function performs. SAS data sets can be classified as numeric and character, therefore SAS functions are often categorized into function handling numeric data (numeric functions) and function handling character data (character functions) and some special functions. Special functions perform special tasks like converting data from one data type to another. Numeric functions can do arithmetic, mathematical, trigonometric, statistical, financial computations, generate random numbers. Character functions perform tasks like searching for strings, replacing strings or joining strings together, extracting a portion of a character value, counting how many words in a sentence. But sometimes, SAS users still cannot perform what they want by using the existing functions. For example, we can use tranwrd()to delete some characters in a string. Suppose we have a string name1, name2, name3, name4, name5, name6, somehow the string was entered like this name1,name2,,,name3,, name4,name5,,,,name6 we want to get rid of the extra, then tranwrd() only cannot do the job. But with the help of PROC FCMP, we can. What is PROC PCMP? PROC FCMP is a gift to SAS users who can use it to write their own functions and CALL routines or subroutines using DATA step syntax. Why it is a gift? Because it is a Base SAS procedure and you don t need to spend extra money on it as long as you have Base SAS. FCMP routines are stored in a SAS catalog and can be called from several SAS/STAT, SAS/ETS, and SAS/OR procedures. In SAS 9.2, FCMP routines can be called from DATA step. SAS users can use the SAS Function Compiler (FCMP) procedure to create, and store SAS functions, and subroutines before using them in other SAS procedures or DATA steps. Most features of the SAS programming language can be used in functions and subroutines. PROC FCMP functions and subroutines can be called from the DATA step just as any other SAS function, or subroutine, making it easier for SAS users to read, write, and maintain complex code with independent and reusable subroutines. The PROC FCMP routines can be reused in any DATA 1

2 step or SAS procedures. And the procedures include GENMOD, MCMC, NLMIXED, PHREG etc. even the Output Delivery System (ODS) Functions are independent computational blocks that require zero or more arguments. A subroutine is a special type of function that has no return value. The function begins with the FUNCTION statement, and the subroutine begins with the SUBROUTINE statement. A single FCMP procedure step can contain several functions and subroutines. The basic syntax is: PRCO FCMP OUTLIB=libname.dataset.package; Function body ; RETURN(expression); ENDSUB; or Subroutine body ; RETURN; ENDSUB; OUTLIB specifies the three-level name of an output data set to which the compiled functions and subroutines are written when the PROC FCMP step ends. And the functions and subroutines are saved in an output library. If the OUTLIB= is not used, then no functions and subroutines that are declared in the current PROC FCMP step are saved. A function body contains a function name, its arguments, and data step (code). The arguments are passed by value, which means that the value of the actual argument, variable, or value that is passed to the function from the calling environment is copied before being used by the function. This copying ensures that any modification of the formal argument by the function does not change the original value. Data step code specifies the tasks to be performed by the function. The RETURN statement is used to return a value to a function. The RETURN statement uses an expression enclosed in parentheses, and contains the value that is returned to the calling environment. The function declaration ends with an ENDSUB statement. The subroutine begins with the SUBROUTINE keyword instead of the FUNCTION keyword. A subroutine body contains a subroutine name, its arguments, and data step (code). The arguments are passed by reference and are listed in the OUTARGS statement, which means that any modification of the argument will modify the original variable that was passed. A RETURN statement in a subroutine does not return a value. Data step code specifies the tasks to be performed by the subroutine. Unlike other SAS procedures or DATA steps, PROC FCMP doesn t take in data by using a data statement nor output data by using output statement. Data is typically transferred into and out of PROC FCMP routines by using parameters. In general, PUT statement can be used to see the results in the log. Now let s come to some examples, 2

3 Suppose we have survey data consisting of 9 questions with values from 1 to 4 each, measuring trust in 9 different things, 1 stands for A lot, 2 some, 3 a little and 4 not at all. Suppose we want to create a new variable TRUST with value of 1(trust, not 4) and 0(not trust, only 4) then we use proc fcmp outlib=sasuser.funcs.trial; function COMP(Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9); COMP= (sum ((Q1 le 3), (Q2 le 3), (Q3 le 3), (Q4 le 3), (Q5 le 3), (Q6 le 3), (Q7 le 3), (Q8 le 3), (Q9 le 3)) = 9); return(comp); endsub; options cmplib=sasuser.funcs; data two; set one; TRUST = comp(q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9); run; outlib=sasuser.funcs.trial; Use this option when you want to save functions and subroutines in an output library. Otherwise functions and subroutines would not be saved.the function in the example is saved to the data set sasuser.funcs inside a package called trial. A package is a collection of related routines that are specified by the user. function COMP(Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9); This statement says the function will perform some operations on this nine variables and the name of operations is called COMP. COMP=(sum ((Q1 le 3), (Q2 le 3), (Q3 le 3), (Q4 le 3), (Q5 le 3), (Q6 le 3), (Q7 le 3), (Q8 le 3), (Q9 le 3)) = 9); This says what exactly the function will be doing. Q le 3 is a logical statement and it returns either 1 if the statement is true: that is Q is less than 3 or 0 if the statement is false: that is Q is not less than 3. If these 9 logical statements are all true, then the sum will be 9, making COMP =1; If one of these 9 logical statements are not true, then the sum will not be 9, making COMP =0. return(comp) will return the value of COMP to the calling environment. endsub is used to close the function. Before the data step, cmplib=sasuser.funcs is specified to tell SAS where to look for the function of COMP. In the data step, the function is called. And the variable TRUST takes the values from COMP. The second example: Suppose we have a string name1,name2,,,name3,, name4,name5,,,,name6 but we only want one comma to separate each name name1, name2, name3, name4, name5, name6, then we can get it done by using proc fcmp outlib=work.myfuncs.char; subroutine decomma(string $); outargs string; string=tranwrd(string,",,",","); if index(string,",,") > 0 then call decomma(string); endsub; quit; options cmplib=work.myfuncs; data _null_; list="namel,name2,,name3,,,name4,name5,,name6,,,,,namex"; call decomma(list); 3

4 put list=; run; outlib=work.myfuncs.char; Use this option when you want to save functions and subroutines in an output library. Otherwise functions and subroutines would not be saved. The subroutine in the example is saved to the data set work.myfuncs inside a package called char. A package is a collection of related routines that are specified by the user. subroutine decomma(string $); This statement says the subroutine will perform some operations on this string and the name of operations is call decomma. Since it is a string, a $ sign must be used. outargs string; After subroutine statement, outargs must be used and the argument in outargs is returned through a reference. string=tranwrd(string,",,",","); if index(string,",,") > 0 then call decomma(string); This says what exactly the subroutine will be doing. TRANWRD function is used to remove repeated commas in text. index(string,",,") > 0 says,, is found. call decomma(string) says remove it. Endsub It is used to close the function. Before the data step, cmplib=work.myfuncs is specified to tell SAS where to look for the subroutine of decomma. In the data step, the subroutine is called to perform the task of removing the extra comma. You can see the results by issuing a PUT statement. The third example: SAS doesn t have some functions that MS Excel has. But they are available by using PROC FCMP and you will find that MS Excel has a vast repertoire of functions. By issuing the following code, those excel functions become handy. PROC FCMP INLIB=sashelp.slkwxl LISTALL; RUN; Here is the list of the functions: Function avedev_slk ( data ) Function devsq_slk ( data ) Function varp_slk ( data ) Function even_slk ( x ) Function factdoule_silk ( x ) Function floor_slk ( n, sg ) Function multinormial_slk ( nums ) Function odd_slk ( x ) Function product_slk ( nums ) Function accrint_slk ( issue, finterest, settlement, rate, par, freq, basis ) Function accrintm_slk ( issue, maturity, rate, par, basis ) Function amordegrc_slk ( cost, datep, fperiod, salvage, period, rate,basis ) Function amorlinc_slk ( cost, datep, fperiod, salvage, period, rate, basis ) Function coupdaybs_slk ( settlement, maturity, freq, basis ) Function coupdays_slk ( settlement, maturity, freq, basis ) Function coupdaysnc_slk ( settlement, maturity, freq, basis ) Function coupncd_slk ( settlement, maturity, freq, basis ) Before you use the excel functions in SAS, you should specify cmplib=sasuser.funcs to tell SAS where to look for the excel function. In the data step, the function is called. For example, you can call product_skl function. The product function multiplies all the numbers given as arguments and returns the product. In SAS, the arguments must take an array in product function. OPTIONS CMPLIB = sashelp.slkwxl; 4

5 DATA _NULL_; array x[5] ( ); product = product_slk(x); PUT 'Product is ' product; RUN; You will see Product is 720 in the log. These three examples have given you an idea about the basics of PROC FCMP. You definitely can create your own functions and make use of Excel functions in SAS now. CONCLUSION This paper covers the very basics of the FCMP procedure. There are more topics about the FCMP procedure, like function editor, SELECT statements in PROC SQL, matrix operation, calling C function, etc. Readers can go to reference material listed below for further study. With the FCMP procedure, you can get more functionalities out of SAS and solve problems otherwise difficult or impossible. REFERENCE SAS Institute Inc The FCMP Procedure. Cary, NC: SAS Institute Inc. Secosky, Jason, 2007, User-Written DATA Step Functions, published in the Proceedings of the SAS Global Forum 2007 Conference, Cary, NC: SAS Institute Inc., CONTACT INFORMATION Your comments and questions are valued and encouraged. Contact the author at: Dachao Liu Northwestern University Suite N Lake Shore Dr. Chicago, IL Phone (312) dachao-liu@northwestern.edu SAS and all other SAS Institute Inc. product or service names are registered trademarks or trademarks of SAS Institute Inc. in the USA and other countries. indicates USA registration. Other brand and product names are trademarks of their respective companies 5