topic Re: Numeric issue in datastep in SAS Programming

Numeric issue in datastep

Q1983 — Thu, 16 Mar 2017 02:06:41 GMT

data test;

set test2;

diff = t1 - t2;

run;

sample data

t1 t2 diff

12 6 6

14191.65 14191.65 1.818989E-12

The issue is whenever I encounter a large number the difference is reflected as scientific notation where as it should be a 0

I used

proc format;

picture mynum

low - high = '000000000009';

run;

The number displays as a 0 however when I apply a test such as

if diff = 0 then delete; The test fails and the row still appears

any ideas

Re: Numeric issue in datastep

Reeza — Thu, 16 Mar 2017 02:17:55 GMT

Welcome to computing 🙂

This is a known 'issue'. Please see the full explanation below.

http://support.sas.com/documentation/cdl/en/lrcon/69852/HTML/default/viewer.htm#p0ji1unv6thm0dn1gp4t01a1u0g6.htm

You can resolve this by formatting your data, using something like 8.1 should be enough.

And you can change your test to:

if round(value, 0.0001) = 0 then <action>;

Re: Numeric issue in datastep

art297 — Thu, 16 Mar 2017 02:20:57 GMT

Just responded to a similar question in a different thread. The topic you want to Google is numeric precision. It's not just with SAS, but any computer.

The numbers are likely to be off somewhere off to the right decimal place. The solution is to round the numbers to the number of decimal points that are practically significant to whatever you're doing.

Art, CEO, AnalystFinder.com

Re: Numeric issue in datastep

Jagadishkatam — Thu, 16 Mar 2017 02:21:54 GMT

Could you please try the below approach

data test;
set test2;
diff = t1 - t2;
format diff mynum.;
if compress(put(diff,best.))='0' then delete;
run;

Re: Numeric issue in datastep

Kurt_Bremser — Thu, 16 Mar 2017 07:22:04 GMT

As the others have already noted, this is an artifact resulting from the way SAS stores numeric values.

Adapt your data step (and other steps that do similar calculations):

data test;
set test2;
diff = round(t1 - t2,.00001);
run;

And you'll get rid of problems caused by precision overflows or numbers that are periodic in binary representation.

Re: Numeric issue in datastep

ballardw — Thu, 16 Mar 2017 14:41:34 GMT

BTW your example data is wrong because you let a very likely default format of best8. display the values of t1 and t2.

I know this because when I copy your pasted example data and use that in a data step the result is 0.

data example;
   x=14191.65;
   y=14191.65;
   result = y-x;
   put result= best32.;
run;

Re: Numeric issue in datastep

Rick_SAS — Thu, 16 Mar 2017 18:17:55 GMT

In addition to what others have said, you should avoid testing floating-point values for equality. Instead, test whether the value is within a small amount of the target value:

if fabs(diff) < 1e-6 then delete;