multiplication in sas

[himself]

Hi, all

   Am having the following code, could someone kindly explain to me why the values of d1 and d2 are missing. Though we have the value of c=1.8.

data mult;
  a=1.2;b=1.5;
  c=a*b;
  if c="1.8" then d1=1;
   if c=1.8 then d2=1;
run;

thanks

[ChrisNZ · Accepted solution]

You need to read about numeric precision. Lots of resources on the web and here.

Summary: the binary system used by computers is perfect for storing powers-of-2 numbers, not so good for storing decimals.

Run this to see the horrid details:

data _null_;
  A=1.5*1.2-1.8;   
  putlog A= 32.16;
run;

A=-0.0000000000000002

[himself]

Hi, @ChrisNZ, thanks for sharing , actually I thought SaS performs the multiplication of decimals as the normal way one can do multiplication, plus the way it stores the values, I have realized its very different

[Amir]

Hi @himself ,

The round() function can be useful in situations like this.

It is documented here and has a discussion and demonstration of the type @ChrisNZ was referring to.

Kind regards,

Amir.

[gamotte]

Hello,

Column c is numeric, why do you compare it to a string ?

To compare floating points numbers, you can do as follows :

%let precision=1.0e-06;

data mult;
  a=1.2;b=1.5;
  c=a*b;
   if abs(sum(c,-1.8))<&precision. then d2=1;
run;