Normalizing dataset with ruby

Question

I have a data set that ranges from 1 to 30,000

I want to normalize it, so that it becomes 0.1 to 10

What is the best method/function to do that?

Would greatly appreciate it if you could give some sample code!

Answer 1

Here's a code snippet, assuming you want a linear normalization. It's a very simplistic version (just straight code, no methods), so you can see "how it works" and can apply it to anything.

xmin = 1.0
xmax = 30000.0
ymin = 0.1
ymax = 10.0

xrange = xmax-xmin
yrange = ymax-ymin

y = ymin + (x-xmin) * (yrange / xrange) 

---

And here it is done as a function:

def normalise(x, xmin, xmax, ymin, ymax)
  xrange = xmax - xmin
  yrange = ymax - ymin
  ymin + (x - xmin) * (yrange.to_f / xrange) 
end

puts normalise(2000, 1, 30000, 0.1, 10) 

(Note: the to_f ensures we don't fall into the black hole of integer division)

Answer 2

Here's the Ruby Way for the common case of setting an array's min to 0.0 and max to 1.0.

class Array
  def normalize!
    xMin,xMax = self.minmax
    dx = (xMax-xMin).to_f
    self.map! {|x| (x-xMin) / dx }
  end
end

a = [3.0, 6.0, 3.1416]
a.normalize!
=> [0.0, 1.0, 0.047199999999999985]

For a min and max other than 0 and 1, add arguments to normalize! in the manner of Elfstrom's answer.

Answer 3

x = x / 3030.3031 + 0.1

Answer 4

This is a well known way to scale a collection numbers. It has more precise name but I can't remember and fail to google it.

def scale(numbers, min, max)
    current_min = numbers.min
    current_max = numbers.max
  numbers.map {|n| min + (n - current_min) * (max - min) / (current_max - current_min)}
end

dataset = [1,30000,15000,200,3000]
result = scale(dataset, 0.1, 10.0)
=> [0.1, 10.0, 5.04983499449982, 0.165672189072969, 1.08970299009967]
scale(result, 1, 30000)
=> [1.0, 30000.000000000004, 15000.0, 199.99999999999997, 3000.0000000000005] 

As you can see, you have to be aware of rounding issues. You should probably also make sure that you don't get integers as min & max because integer division will damage the result.