Numeric division less than or greater than error

[newboy1218]

Hi, I am trying to calculate the % of A debt amount within the sum of A + B debt amount, and then I want to filter out % of A debt amount is between 90 - 100% (excluding 90% and 100%). However, in my result, it return answer where a_debt_pcent = 100.. Do you know why even though I excluded 100%?

Thanks.

data aa;
	input a_debt_amt b_debt_amt; 
	datalines;
	10701.54 0
	84256.96 0
	21462.54 0
	240 20
	23876.83 0
	95 5
	396 184
	982 3874
	0 9128
;
run;

data bb;
	set aa;
	a_debt_pcent = 100*a_debt_amt/(a_debt_amt+b_debt_amt);
	if 90 < a_debt_pcent < 100;
run;

WANT:

a_debt_amt	b_debt_amt	a_debt_pcent
240	20	92.307692308
95	5	95

What I am getting (I don't want that, it is wrong):

a_debt_amt	b_debt_amt	a_debt_pcent
10701.54	0	100
84256.96	0	100
240	20	92.307692308
23876.83	0	100
95	5	95

[mkeintz · Accepted solution]

You have run into a numeric precision problem that arises from floating point calculations. This is NOT a SAS problem.  It is a problem of numeric representation on digital computers.

In effect, your statement:

	a_debt_pcent = 100*a_debt_amt/(a_debt_amt+b_debt_amt);

is calculated like this

	a_debt_pcent = (100*a_debt_amt)/(a_debt_amt+b_debt_amt);

That is, it makes the product  100*a_debt_amt for the numerator first, then sums a_debt_amt and b_debt_amt for denominator, then divides.  The problem is that the numeric representation of 100*a_debtamt, will not always yield a value of 100 when divided by a_debt_amt  (i.e. when b_debt_amt=0).  You will see "100" because it is not printing with enough precision to show the very minor difference from 100 that might occur.

Change the statement to 

	 a_debt_pcent = 100* (a_debt_amt/(a_debt_amt+b_debt_amt));

Then you will always get 100 when b_debt_amt is zero.  

[average_joe]

Round your percent calculation to the nearest whole number like this:

	a_debt_pcent = round(100*a_debt_amt/(a_debt_amt+b_debt_amt), 1);

The reason has to do with numeric precision and floating point math. You can read about it here.

Try this as another example:

data _null_;
num = .1 * 3;

if num = .3 then put '1. Equal';
else put '1. Not Equal';

if round(num, .1) = .3 then put '2. Equal';
else put '2. Not Equal';
run;

[Sajid01]

Hello @newboy1218 

Simple and self-explanatory changes to your code will give you the desired result.

Your a_dept_pcent is a floating point number. Hence the small changes to your expressions..

data bb;
	set aa;
	a_debt_pcent = round((100*a_debt_amt)/(a_debt_amt+b_debt_amt),2);
	format a_debt_pcent z6.3;
	if 90.000 < a_debt_pcent < 100.000;
run;

The output is what you want