Find max value in a sparse javascript array

Question

Is there a proper way to find the max value of a sparse array with undefined values?

Thanks

var testArr=[undefined,undefined,undefined,3,4,5,6,7];
console.log('max value with undefined is ',(Math.max.apply(null,testArr)));

// max value with undefined is NaN

console.log('max with arr.max()',testArr.max());    

// Error: testArr.max is not a function     

testArr=[null,null,null,3,4,5,6,7];
console.log('max value with null is ',(Math.max.apply(null,testArr)));

// max value with null is 7

I'd prefer not to do forEach if there is a built-in method.

Math.max attempts to convert its arguments to numbers. Since undefined is converted to NaN (ecma-international.org/ecma-262/5.1/#sec-9.3) it will fail with those values. You'll have to iterate over the values. The closest thing to "built-in" is Array.reduce. — Daniel Weiner
– Daniel Weiner, Commented Jan 20, 2015 at 22:03
Also, null is converted to 0 so you'll get the wrong answer if your array is filled with nulls and negative numbers. — Daniel Weiner
– Daniel Weiner, Commented Jan 20, 2015 at 22:15

Daniel Weiner · Accepted Answer · 2015-01-20 22:49:37Z

2

testArr.reduce(function(a,b){
  if (isNaN(a) || a === null || a === '') a = -Infinity;
  if (isNaN(b) || b === null || b === '') b = -Infinity;
  return Math.max(a,b)
}, -Infinity);

edited Jan 20, 2015 at 22:49

answered Jan 20, 2015 at 21:55

Daniel Weiner

1,9041 gold badge12 silver badges19 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Xotic750 Over a year ago

Empty strings with negative numbers would be an issue as it stands.

Daniel Weiner Over a year ago

Good catch, I just updated my solution to account for empty strings.

Xotic750 · Accepted Answer · 2015-01-20 22:49:54Z

2

None of your examples are true sparse arrays (they don't have any 'holes'), but you could use Array.prototype.filter (ECMA5) to test the value isFinite. For better accuracy ECMA6 will offer Number.isFinite. Remember there are also limits to the number of arguments that Function.prototype.apply can handle (often 65536 arguments). Of course, isFinite may not be suitable for your application, if you want Infinity and -Infinity, then you should use a different test. An empty string with negative numbers would be an issue in this current exampe.

var testArr = [undefined, , , 3, 4, 5, 6, 7];

document.body.textContent = Math.max.apply(null, testArr.filter(function (x) {
    return isFinite(x);
}));

edited Jan 20, 2015 at 22:49

answered Jan 20, 2015 at 22:12

Xotic750

23.6k8 gold badges59 silver badges81 bronze badges

2 Comments

georg Over a year ago

Simply testArr.filter(isFinite)

Xotic750 Over a year ago

@georg Yes indeed, I was thinking that having it verbose may be better for the answer as it is not clear that isFinite is the best check for the question raised.

Collectives™ on Stack Overflow

Find max value in a sparse javascript array

2 Answers 2

2 Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related