Explain: Min/Max array with infinity

Question

I was looking into how to find the min and max value in an array (without using Math) and I came across this code in a forum:

var array = [4, 2, 3, 4]
var min = arrayMin(array);
out.innerHTML = min;

function arrayMin(arr) {
  var len = arr.length, min = Infinity;
  while (len--) {
    if (arr[len] < min) {
      min = arr[len];
    }
  }
  return min;
};

<p id="out"></p>

I can't really wrap my head around it and understand it fully, especially the infinity part. Could someone be so nice and explain it as simple as possible?

The variable `min` keeps track of the smallest value seen so far. When a value from the array is smaller than that, it becomes the new minimum. — Pointy, Sep 23 '18 at 13:39
everything seems as expected except `out.innerHTML = min;` line — A l w a y s S u n n y, Sep 23 '18 at 13:40
The value `Infinity` is bigger than any other number. By starting out with that as the smallest value, the actual numbers in the array will all be tested. Imagine if it started out with `min = 100;` instead. Do you see why that would not work in some cases? — Pointy, Sep 23 '18 at 13:42
@Karen hope the answers clear it up , if not you can comment. I will help — ashish singh, Sep 23 '18 at 13:43
a nice workaround is to use the first element and run the loop from index one. — Nina Scholz, Sep 23 '18 at 14:15

score 3 · Answer 1 · answered Sep 23 '18 at 13:42

The logic seems to be fine. The code you have added gives minimum value. min is initialised to Infinity and min is updated as you traverse through array.

Lets take a look at what happens for first array element.

4 < Infinity //index = 0 min becomes 4
2 < 4 //index = 1 min becomes 2

and so on the code will output minimum value.

Adam Chubbuck · Answer 2 · 2018-09-23T13:48:50.870

Infinity is a property of the global object, or in other words, a variable in global scope.

The initial value of Infinity is Number.POSITIVE_INFINITY. The value Infinity (positive infinity) is greater than any other number. Mathematically, this value behaves the same as infinity; for example, any positive number multiplied by Infinity equals Infinity, and any number divided by Infinity equals 0.

So, what the above function is doing is creating a temporary variable called min that keeps track of the smallest number. When the first comparison is made, it will overwrite the value of min every time since Infinity is higher than any other number. Then, it continues to iterate through the array making the same evaluation until it exits.

Here is an inline snippet demonstrating how this works:

var array = [4, 2, 3, 4]
var min = arrayMin(array);

function arrayMin(arr) {
  var len = arr.length, min = Infinity;
  while (len--) {
    console.log(min);
    if (arr[len] < min) {
      min = arr[len];
    }
  }
  return min;
};

You can read more about Infinity here.

Explain: Min/Max array with infinity

2 Answers2