Distribute array values so maximum will be 1 and minimum will be 0

Question

I think this must be a basic math operation but I really can't figure it out. I need to get an array of values between 0 and 1 based on values from a given array. So, for example, if we have an initial array [24, 128, 52] the resulting array should be [0, 1, 0.5]. Maximum and minimum values should be always be 1 and 0 respectively and the rest should be proportionately in between them.

How can I do this in Swift?

Answer 1

Start with an array:

let sourceArray = [24.0, 128.0, 52.0]

Store the minimum and maximum elements:

let min = minElement(sourceArray) // 24.0
let max = maxElement(sourceArray) // 128.0

Normalize each element and map the results to a new array:

let results = sourceArray.map { ($0 - min) / (max - min) }

results is:

[0, 1, 0.2692307692307692]

You specified you wanted [0, 1, 0.5], but I think that's wrong, since you said "the rest should be proportionately in between them". Inputting [24.0, 128.0, 76.0] would output [0, 1, 0.5].

Note: the source array can't be [Int] or the map operation will round the result to either 1 or 0. If you need to work with [Int] you'll have to convert each element in the map operation.