Convert large numbers to smaller format

Int+Extenstion.swift

import Foundation

extension Int {
  func abbreviate() -> String {
    typealias Abbrevation = (threshold: Double, divisor: Double, suffix: String)

    let abbreviations: [Abbrevation] = [
      (0, 1, ""),
      (1000.0, 1000.0, "K"),
      (100_000.0, 1_000_000.0, "M"),
      (100_000_000.0, 1_000_000_000.0, "B"),
      (100_000_000_000.0, 1_000_000_000_000.0, "T")
    ]

    let startValue = Double (abs(self))

    let abbreviation: Abbrevation = {
      var prevAbbreviation = abbreviations[0]

      for tmpAbbreviation in abbreviations {
        if (startValue < tmpAbbreviation.threshold) {
          break
        }

        prevAbbreviation = tmpAbbreviation
      }

      return prevAbbreviation
    }()

    let formatter = NumberFormatter()
    formatter.positiveSuffix = abbreviation.suffix
    formatter.negativeSuffix = abbreviation.suffix
    formatter.allowsFloats = true
    formatter.minimumIntegerDigits = 1
    formatter.minimumFractionDigits = 0
    formatter.maximumFractionDigits = 1

    let value = Double(self) / abbreviation.divisor

    return formatter.string(from: NSNumber(value: value))!
  }
}

Example

let testValues: [Int] = [
  598,
  -999,
  1_000,
  -1_284,
  9_940,
  9_980,
  39_900,
  99_880,
  399_880,
  999_898,
  999_999,
  1_456_384,
  12_383_474
]

testValues.forEach() {
  print("Value : \($0) -> \($0.abbreviate())")
}

Output

Value : 598 -> 598
Value : -999 -> -999
Value : 1000 -> 1K
Value : -1284 -> -1.3K
Value : 9940 -> 9.9K
Value : 9980 -> 10K
Value : 39900 -> 39.9K
Value : 99880 -> 99.9K
Value : 399880 -> 0.4M
Value : 999898 -> 1M
Value : 999999 -> 1M
Value : 1456384 -> 1.5M
Value : 12383474 -> 12.4M