How to normalize a list of positive numbers in JavaScript?

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!

Answers:

Answer

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

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
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

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

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

Answer

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

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)

enter image description here

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