How to normalize a list of positive numbers in JavaScript?

Question

I have an array filled with positive int values, how could I normalize this list so the max value is always 100? Thank you in advance!

Answer 1

The idea is to first find the highest number in your array (using apply on Math.max), then find the ratio between that highest number and 100.

After that, it's just a matter of looping through your array and dividing all your numbers by that ratio:

var numbers = [3, 8, 45, 74, 123],
    ratio = Math.max.apply(Math, numbers) / 100,
    l = numbers.length,
    i;

for (i = 0; i < l; i++) {
    numbers[i] = Math.round(numbers[i] / ratio);
}

Here's the fiddle: http://jsfiddle.net/XpRR8/

---

Note: I'm using Math.round to round the numbers to the nearest integer. If you instead prefer to keep them as floats, just remove the function call:

for ( i = 0; i < l; i++ ) {
    numbers[i] /= ratio;
}

Here's the fiddle: http://jsfiddle.net/XpRR8/1/

---

If you don't have to support IE8 and below, you can use Array.prototype.map():

var numbers = [3, 8, 45, 74, 123],
    ratio = Math.max.apply(Math, numbers) / 100;

numbers = numbers.map(function (v) {
    return Math.round(v / ratio);
});

Here's the fiddle: http://jsfiddle.net/XpRR8/2/

---

If you do support IE8, but are anyhow using jQuery, you can use $.map() instead:

numbers = $.map(numbers, function (v) {
    return Math.round(v / ratio);
});

Here's the fiddle: http://jsfiddle.net/XpRR8/3/

---

Update: As pointed out by @wvxvw in the comments below, if you're concerned about fringe implementations that impose an artificial limit on the amount of arguments apply will handle, then use a loop instead of Math.max.apply. Here's an example (assuming neither Array.prototype.map nor $.map are available):

var numbers = [3, 8, 45, 74, 123],
    ratio = 0,
    i = numbers.length;

while (i--) numbers[i] > ratio && (ratio = numbers[i]);

ratio /= 100;
i = numbers.length;

while (i--) numbers[i] = Math.round(numbers[i] / ratio);

Here's the fiddle: http://jsfiddle.net/XpRR8/4/

---

If you're using ES6, this becomes laughably simple:

var numbers = [3, 8, 45, 74, 123];
var ratio = Math.max(...numbers) / 100;

numbers = numbers.map(v => Math.round(v / ratio));

Answer 2

Like this

function Normalize(array, value)
{ 
 for( var i = 0, len = array.length; i < len; i++ )
 {
  if( parseInt(array[i]) > value) array[i] = value;
 }
}

And then use it:

var arr = [];
arr.push(101);
arr.push(5);
arr.push(6);
Normalize(arr,100);

Answer 3

function normalize(arr, max) {
    // find the max value
    var m = 0;
    for(var x=0; x<arr.length; x++) m = Math.max(m, arr[x]);
    // find the ratio
    var r = max / m;
    // normalize the array
    for(var x=0; x<arr.length; x++) arr[x] = arr[x] * r;
    return arr;
}

Answer 4

Well, you can get the maximum value with Math.max.apply(arr), then either loop through or use arr.map to multiply all numbers by 100/max. Done.

Answer 5

You need to find the maximum and scale all numbers to the target range.

Answer 6

Just an edit to LastCoder code to support Negative numbers as well

function normalize(arr, max) {
    // find the max value
    var max = arr[0];
    var min = arr[0];
    for(var x=0; x<arr.length; x++) 
        max = Math.max(m, arr[x];
    for(var x=0; x<arr.length; x++) 
        min = Math.min(m, arr[x];

    // normalize the array
    for(var x=0; x<arr.length; x++) 
        arr[x] = (arr[x] - min) / (max - min);

    return arr;
}

Answer 7

Pass your array into the following function:

function normalize_array(arr) {

  normalize = function(val, max, min) { 
    return(val - min) / (max - min); 
  }

  max = Math.max.apply(null, arr) 
  min = Math.min.apply(null, arr)

  hold_normed_values=[]
  arr.forEach(function(this_num) {
    hold_normed_values.push(normalize(this_num, max, min))
  })

  return(hold_normed_values)

}

Example:

nums = [10, 20, 30, 40, 50]

Usage:

normalize_array(mums)