IRR function from IML

model_coder — Thu, 19 Nov 2009 17:00:13 GMT

Is it possible to call IRR function from IML?

Re: IRR function from IML

Rick_SAS — Thu, 19 Nov 2009 21:33:06 GMT

Yes, you can.

I'll present a general technique for writing a module that "wraps" a Base SAS function so that it becomes "vectorized." (This technique is adapted from code that will appear in my forthcoming book Statistical Programming with SAS/IML Software: An Introduction, SAS Press, 2010.)

The issue, for those not familiar with calling Base SAS functions, is that some Base SAS functions string out their arguments in a list, whereas in SAS/IML it is convenient to be able to pass a vector of values. For the case of the IRR function, you can call IRR from IML explicitly by forming a list:

proc iml;
/* call Base SAS function directly to find the answer */
rate1 = IRR(1,-400,100,200,300);
print rate1;

However, in SAS/IML the parameters are typically in a vector such as
c = {-400,100,200,300};
and you cannot call IRR as
rate2 = IRR(1,c); /* WRONG! Can't send vector to function expecting a list */

How can we call the Base SAS function? The key is to define a module that uses the PUTN function to convert the numeric parameters to a long, comma, separated list, then call the EXECUTE subroutine.

/* Call the IRR function in Base SAS.
This technique works for any Base SAS function that
is expecting a list of arguments instead of a vector.
Rick Wicklin */
start myIRR(freq, c);
/* convert numeric matrices a single string */
args = strip(putn(freq,"BEST12.")); /* string of the freq value */
cc = strip(putn(c, "BEST12.")); /* character vector of c */
do i = 1 to nrow(cc)*ncol(cc); /* concatenate all values */
args = concat(args, ",", strip(cc));
end;
cmd = "rate = IRR(" + args + ");" ; /* Base function call, as a string */
call execute(cmd); /* execute the string */
return (rate); /* return result from Base SAS function */
finish;

freq = 1;
c = {-400,100,200,300};
rate = myIRR(freq,c); /* call Base SAS function with vector */
print rate;

Re: IRR function from IML

model_coder — Fri, 20 Nov 2009 18:43:14 GMT

Thanks Rick. This was very helpful.

Re: IRR function from IML

model_coder — Fri, 20 Nov 2009 21:12:01 GMT

I have it working now after a small fix in the code. Message was edited by: model_coder

Re: IRR function from IML

Rick_SAS — Fri, 05 Mar 2010 13:24:32 GMT

As model_coder mentions, there is a typo in the program.
The statement inside the DO loop should say:
args = concat(args, ",", strip(cc));

Re: IRR function from IML

Rick_SAS — Fri, 05 Mar 2010 13:26:21 GMT

Rats: The blog software seems to "eat" certain character sequences. Very annoying.
The statement inside the DO loop should say:
args = concat(args, ",", strip(cc [ i ])); /* LEFT_BRACKET i RIGHT_BRACKET */

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