CODEWITHSUNDEEP
javascript
David Garcia
David Garcia

Reputation: 2696

Javascript: percentage difference between two values

I am using the following javascript code to display the difference in percentage between two values.

A = 11192;
B = 10474;

percDiff = (vars.A - vars.B) / vars.B * 100;

Which gives: 6.855069696391064

Then

if (percDiff > 20) {
  //dosomething
} else {
  //dosomething
}

The problem is:

If value B is higher than value A then i get a NaN, for instance; NaN

How can I overcome this issue? I thought about using Math.abs()

Any suggestions?

Upvotes: 16

Views: 34874

Answers (4)

hassan zarghami
hassan zarghami

Reputation: 179

function calculatePercentageDifference(valueA, valueB) {
  const difference = valueB - valueA;
  const percentageDifference = Math.abs((difference / valueA) * 100);
  return percentageDifference;
}

// Example values
const valueA = 50000;
const valueB = 80000;

const percentDiff = calculatePercentageDifference(valueA, valueB);
console.log(percentDiff); // Output: 60

Upvotes: 0

KooiInc
KooiInc

Reputation: 122916

I think you can use this formula to determine the relative difference (percentage) between 2 values:

var percDiff =  100 * Math.abs( (A - B) / ( (A+B)/2 ) );

Here's a utility method:

function relDiff(a, b) {
 return  100 * Math.abs( ( a - b ) / ( (a+b)/2 ) );
}
// example
relDiff(11240, 11192); //=> 0.42796005706134094

Note for people thinking the answer provides a wrong result: this question/answer concerns percentage difference1, not percentage change2.

Here's a snippet to demonstrate the difference (pun intended;)

const relativePercentageDifference = (a, b) => 
  Math.abs( ( ( a - b ) / ( ( a + b ) / 2 ) ) * 100 );
const percentageChange = (a, b) => ( b / a * 100 ) - 100;
console.log(`relative % difference 2000 - 1000: ${
  relativePercentageDifference(2000, 1000).toFixed(2)}%`);
console.log(`% change 2000 - 1000: ${
  percentageChange(2000, 1000).toFixed(2)}%`);
console.log(`relative % difference 1000 - 2000: ${
  relativePercentageDifference(1000, 2000).toFixed(2)}%`);
console.log(`% change 1000 - 2000: ${
  percentageChange(1000, 2000).toFixed(2)}%`);

JsFiddle

1 The percentual difference between two values divided by the average of the two values.

2 The percentual difference (in-/decrease) between two numbers divided by the original number.

Upvotes: 38

Sergey
Sergey

Reputation: 355

in the case when we need to know the difference of some number to the etalon number:

function percDiff(etalon, example) {
  return  +Math.abs(100 - example / etalon * 100).toFixed(10);
}
// example
percDiff(11240, 11192); //=> 0.4270462633
percDiff(1000, 1500); //=> 50
percDiff(1000, 500); //=> 50

Upvotes: 1

Mathanolwin
Mathanolwin

Reputation: 31

diffPercent = function(a, b) {
 return  ( a<b ? "-" + ((b - a) * 100) / a : ((a - b) * 100) / b ) + "%";
}

Upvotes: 1

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