topic Re: Strange result using lt comparison operator in SAS Programming

Strange result using lt comparison operator

SP_SAS — Tue, 04 Aug 2015 18:40:18 GMT

Hi There,

If I run the below data step I see SAS behaving in strange manner. Variable y resolves to 1.2. SAS thinks x(1.2) is less than y. Any help will be appreciated.

Thanks,

Santosh

data aa;

x=1.2;
y=(1.1+1*0.1);
if x<y then Confused="Yes";
else Confused="No";
run;

Re: Strange result using lt comparison operator

PGStats — Tue, 04 Aug 2015 19:12:24 GMT

SAS numbers are represented internally by floating point values. 1.2 doesn't have an exact representation as a floating point number, so its internal value is an approximation. That approximation will take different values depending on how it was arrived at. Add the following statements and see what happens

if round(x, 0.1) < round(y, 0.1) then RoundConfused="Yes";

else RoundConfused="No";

Re: Strange result using lt comparison operator

Tom — Tue, 04 Aug 2015 20:50:25 GMT

Use the HEX16. format to look at how these two different numbers end up getting stored into the 8 byte IEEE floating point format.

data aa;

x=1.2;

y=(1.1+1*0.1);

put (x y) (= hex16. /) ;

x=round(x,0.1);

y=round(y,0.1);

put / (x y) (= hex16. /) ;

run;

x=3FF3333333333333

y=3FF3333333333334

x=3FF3333333333333

y=3FF3333333333333

run;

Re: Strange result using lt comparison operator

ChrisNZ — Wed, 05 Aug 2015 03:29:52 GMT

Much reading available on this topic.

For example:

Numerical Accuracy in SAS Software: SAS(R) 9.4 Language Reference: Concepts, Fifth Edition

Re: Strange result using lt comparison operator

SP_SAS — Wed, 05 Aug 2015 13:36:19 GMT

Thanks to you all for your quick help.

Santosh